Here is a great short 6 minute video that goes over the 5 pillars of Adwords success.
1) Structure your Adwords account.
2) Choose the right keywords and keep testing them.
3) Write attention-grabbing ads and continually test your ads. Always have at least 2 ads running to test conversion and click through rates of different copy.
4) Select the right landing pages. We would even take this one step further and say you should create landing pages for specific products or services.
5) Track who became your customers.