When and how much flour do I add when mixing dough? I am a rookie bread baker and I have been following some recipes that range in amounts of water and flour. I have a Kitchenaid artisan mixer that has been doing the hard work of kneading for me. My problem is knowing when to stop adding flour during mixing/kneading.

Some recipes say add flour until the dough is workable and then knead. My questions is, when they say use 2 1/2 to 3 1/2 cups of flour but no more. How do I know when to stop, I have ruined a few loaves as they came out heavy and dense.

How do I know when to stop adding flour and let the gluten take care of the stickiness? I often find myself adding flour until the dough balls up and pulls from the sides but by then it's too late.

On the other side, I have kneaded for 15 - 20 minutes waiting for the dough to pull sides of the bowl and it never happened.

When do I add flour and when do I just wait?

Any help or suggestions are greatly appreciated!
I'll convert my comment into an answer, based on your request for help or suggestions.  Bread formulas are created using the "Baker's Percentage Method".  It is expressed in the amount of liquid in ratio to the amount of flour.  This percentage varies according to the style of bread, but within each style produces accurate results when using weight measurement.  

Using volumetric measurement, especially for flour, is highly inaccurate because many variables can influence how much flour fits into a measuring cup (grind, humidity, compaction...etc).  That is why these kinds of recipes often suggest a range, and put the baker in the position of guessing.

Using a scale, and weighing your ingredients according to the baker's percentage of a recipe, removes the guess work.