One of the biggest things I have learned about growing any business is that it takes constant effort. If you stop investing your time, so do your customers. You need to be continually improving and adapting what you have in order to provide the best experience for you and your customers.
When you set up a campaign it will monitor your results automatically, but most of the magic happens when you really pay attention to the results and use them to improve. Check out this piece on improving. Not only do you need to keep an eye on how people are responding to your ads, you need to enhance their experience.
You need to improve your web site as well. We all know that the only thing constant is change. Your customers change too. Check out this piece on improving your pages.
Refined Ad Groups
I have found that I needed to continually refine my ad campaign. I have split and mixed many ad groups and their ads. And I have seen improvements! It is very exciting to see that graph rise. I can see that having very tightly themed ad groups makes a huge difference.