Provide me with some areas I should focus on when turning down a job offer. Also include a short example of how I can incorporate it into my response.
No problem. I can help you with that. Here's where I think you should focus and some examples that can help you out.

1. Be clear and honest with the response - Honesty goes a long way, especially when turning down a job offer, and you also want to be clear in your reasoning. Doing this will help prevent any misunderstandings and closes the door to any issues that could happen in the future. An example of being honest and clear in a reply would be, "I appreciate the offer for [Job Title], but unfortunately, the responsibilities and salary seem to not align with my expectations."
2. Make sure the explanation is reasonable - when explaining why you're turning down the position, you'll want to be sure all information you give them is relevant to the offer. The explanation doesn't need to be anything extensive, being brief and to the point would be better in this instance. One way you could incorporate this into a reply would be, "Thank you for the opportunity, however after much consideration, I feel I would not be a good fit for this position."  
3. Be Polite and Professional - It's best to stay away from any negative comments you may have regarding the position or company. Respect will go a long way in this instance, and keeping a positive tone will help maintain a positive relationship with the company if you ever consider them in the future. A good way to incorporate this would be, "I appreciate you selecting me as a candidate for this position and the time and effort you've put in the reach out to me. Even though I've decided to go another direction, I hope we can maintain a positive relationship for potential future considerations."