buying a stock while the price is going down, and buy it at a lower price
"If you bought them, you can sell them.  That does not preclude you from buying again later. You might get yourself into a situation where you need to account for a so-called ""wash sale"" on your taxes, but your broker should calculate that and report it on your 1099-B at the end of the year.  There's nothing illegal about this though - It's just a required step in the accounting of capital gains for tax purposes." In the US, it is perfectly legal to execute what you've described. However, since you seem to be bullish on the stock, why sell? How do you KNOW the price will continue downwards? Aside from the philosophical reasoning, there can be significant downside to selling shares when you're expecting to repurchase them in the near future, i.e. you will lose your cost basis date which determines whether or not your trade is short-term (less than 1 year) or long-term. This cost basis term will begin anew once you repurchase the shares. IF you are trying to tax harvest and match against some short-term gains, tax loss harvesting prior to long-term treatment may be suitable. Otherwise, reexamine your reasoning and reconsider the sale at all, since you are bullish. Remember: if you could pick where stock prices are headed in the short term with any degree of certainty you are literally one of a kind on this planet ;-).  In addition, do remember that in a tax deferred account (e.g. IRA) the term of your trade is typically meaningless but your philosophical reasoning for selling should still be examined.
If your stock is rising and you want to buy on a dip, the best way to do this is by looking at the chart and incorporating simple Technical Analysis techniques. Firstly, an uptrend is defined as a price chart with higher highs and higher lowers. If you get a lower high or a lower low (or both), it could be the end of the uptrend - be cautious. This can be seen on the chart below with an uptrend line drawn.  If you draw a trend line you can wait for the price to approach the trend line, bounce off it and start moving up again to buy your stock on a dip. If instead the price closes below the trend line, be very cautious - this could be the end of the uptrend and the start of a downtrend - no telling how low the price will go. If this is the case you can then draw a downtrend line and wait for the price to close above the downtrend line before making your purchase. A bid is an offer to buy something on an order book, so for example you may post an offer to buy one share, at $5. An ask is an offer to sell something on an order book, at a set price. For example you may post an offer to sell shares at $6. A trade happens when there are bids/asks that overlap each other, or are at the same price, so there is always a spread of at least one of the smallest currency unit the exchange allows. Betting that the price of an asset will go down, traditionally by borrowing some of that asset and then selling it, hoping to buy it back at a lower price and pocket the difference (minus interest). So, let's say as per your example you borrow 100 shares of company 'X', expecting the price of them to go down. You take your shares to the market and sell them - you make a market sell order (a market 'ask'). This matches against a bid and you receive a price of $5 per share. Now, let's pretend that you change your mind and you think the price is going to go up, you instantly regret your decision. In order to pay back the shares, you now need to buy back your shares as $6 - which is the price off the ask offers on the order book. Because of this spread, you have lost money. You sold at a low price and bought at a high price, meaning it costs you more money to repay your borrowed shares. So, when you are shorting you need the spread to be as tight as possible. It might seem like the PE ratio is very useful, but it's actually pretty useless as a measure used to make buy or sell decisions, and taken largely on its own, pretty useless becomes utterly and completely useless. Stocks trade at prices based on future expectations and speculation, so that means if traders expect a company to double its profits next year, the share price could easily double (there are reasons it might not increase so much, and there are reasons it could increase even more than that, but that's not the point). The Price is now double, but the Earnings is still the same, so the PE ratio is double, and this doubling is based on something some traders know, or think they know, but other traders might not know or not believe! Once you understand that, what use is a PE ratio really? The PE ratio of a company might be low because it is in a death spiral, with many traders believing it will report lower and lower profits in years to come, and the lower the PE ratio of a given company gets probably, relatively, the more likely it is to go bust! If you buy a stock with a low PE ratio you must do so because you feel you understand the company, understand why the market is viewing it negatively, believe that the negativity is wrong or over done, and believe that it will turn around. Equally a PE ratio might be high, but be an excellent buy still because it has excellent growth prospects and potential even beyond what is priced in already! Lets face it, SOMEONE has been buying at the price that's put that PE ratio where is is, right? They might be wrong of course, or not! Or they might be justified now but circumstances might change before earnings ever reach the current priced in expectation. You'll know next year probably! To answer your actual question... first you should now understand there is no such thing as a stock that is on sale, just stocks that are priced broadly according to the markets consensus on its value in years to come, the closest thing being a stock that is 'over sold' (but one man's 'over sold' is another man's train crash remember)... so what to actually look for? The only way to (on average) make good buy and sell decisions is to know about investing and trading (buy some books, I have 12), understand the businesses you propose to invest in and understand their market(s) (which may also mean understanding national and international economics somewhat). "If the price used to be 2.50 but by the time you get in an order it's 2.80, you're going to have to pay 2.80. You can't say, ""I want to buy it at the price from an hour ago"". If you could, everybody would wait for the price to go up, then buy at the old price and have an instant guaranteed profit. Well, except that when you tried to sell, I suppose the buyer could say, ""I want to pay the lower price from last July"". So no, you always buy or sell at the current price. If you submit an order after the markets close, your broker should buy the stock for you as soon as possible the next morning. There's no strict queue. There are thousands of brokers out there, they don't take turns. So if your broker has 1000 orders and you are number 1000 on his list, while some other broker has 2 orders and number 1 is someone else wanting to buy the same stock, then even if you got your order in first, the other guy will probably get the first buy. LIFO and FIFO refer to any sort of list or queue, but don't really make sense here. When the market opens a broker has a list of orders he received overnight, which he might think of as a queue. He presumably works his way down the list. But whether he follows a strict and simple first-in-first-out, or does biggest orders first, or does buys for stocks he expects to go up today and sells for stocks he expects to go down today first, or what, I don't know. Does anybody on this forum know, are there rules that say brokers have to go through the overnight orders FIFO, or what is the common practice?" By buying the call option, you are getting the benefit of purchasing the underlying shares (that is, if the shares go up in value, you make money), but transferring the risk of the shares reducing in value. This is more apparent when you are using the option to offset an explicit risk that you hold. For example, if you have a short position, you are at unlimited risk of the position going up in value. You could decide you only want to take the risk that it might rise to $X. In that case, you could buy a call option with $X strike price. Then you have transferred the risk that the position goes over $X to the counterpart, since, even if the shares are trading at $X+$Y you can close out the short position by purchasing the shares at $X, while the option counterpart will lose $Y. Because buying at discount provides a considerable safety of margin -- it increases the likelihood of profiting. The margin serves to cushion future adverse price movement. Why is so much effort made to get a small percentage off an   investment, if one is then willing to let the investment drop another   20% or more with the reason of being in it for the long term? Nobody can predict the stock price. Now if a long term investor happens to buy some stocks and the market crashes the next day, he could afford to wait for the stock prices to bounce back. Why should he sells immediately to incur a definite loss, should he has confidence in the underlying companies to recover eventually? One can choose to buy wisely, but the market fluctuation is out of his/her control. Wouldn't you agree that he/she should spend much efforts on something that can be controlled? I think the advice Bob is being given is good. Bob shouldn't sell his investments just because their price has gone down. Selling cheap is almost never a good idea. In fact, he should do the opposite: When his investments become cheaper, he should buy more of them, or at least hold on to them. Always remember this rule: Buy low, sell high. This might sound illogical at first, why would someone keep an investment that is losing value? Well, the truth is that Bob doesn't lose or gain any money until he sells. If he holds on to his investments, eventually their value will raise again and offset any temporary losses. But if he sells as soon as his investments go down, he makes the temporary losses permanent. If Bob expects his investments to keep going down in the future, naturally he feels tempted to sell them. But a true investor doesn't try to anticipate what the market will do. Trying to anticipate market fluctuations is speculating, not investing. Quoting Benjamin Graham: The most realistic distinction between the investor and the speculator is found in their attitude toward stock-market movements. The speculator's primary interest lies in anticipating and profiting from market fluctuations. The investor's primary interest lies in acquiring and holding suitable securities at suitable prices. Market movements are important to him in a practical sense, because they alternately create low price levels at which he would be wise to buy and high price levels at which he certainly should refrain from buying and probably would be wise to sell. Assuming that the fund in question is well-managed, I would refrain from selling it until it goes up again. Yes  You could write a covered call and the stock gets called away at the price + premium.  You could convince someone to buy it regardless of the market price.