Amazon Associate Mistakes
Unfortunately there are a few people that are unsuccessful in there campaign to sell items online. You can learn from some of the mistakes here.
Trademark issues are quite serious and breaking trademarks means that you can see yourself being banned. Ensure you do not have "Amazon" in your URL if you are selling things online, as they will think you are trying to use their name to maximise your profits.
Ignorance is not a viable excuse from not knowing what you can and can't do. Ensure you read the TOS and know your limit for what you can do within your site.

Under no circumstance must you manually change the code that Amazon gives you when you have customised your products. This is a breach of TOS and will lead to you being banned.
Clutterd sites that are ugly will not produce sales. Look into streamlining your site to give it a pleasant feel. You want your visitors to feel welcome.
Forcing the products onto customer leads to them leaving your site. You have to persuade your visitors to buy from you, and this means blending your products so that they do not appear obtrusive.
Far too many people realise that Amazon is a great way to make more money online and think that is an easy job. This is a common misconception. To be successful you need to carefully plan where you are going to place these products within your site and ensure that you work on updating content within the site. Making your visitors trust the site is important, so creating a professional look is a great start. There are too many dated sites which simply do not work, there is no excure to produce a dated site with so much new technology around and cheap web designers that can create stunning sites.