Optimizing you site is all about trial and error. There are many ways to test things out without messing up your whole site. Google AdWords lets you organize your ads in ways to help you find what is most effective. For example, you start with one campaign. Within that campaign you can have different ad groups. These can be made for each section or topic of your site. Within each ad group it allows you to set keywords up with specific ads. You can have more than one ad for each set of keywords so you can more easily see which ad is bringing in more customers.
Key Words
There are different ways to optimize keywords also. You can make a word broad match, which means if that word is in a search you ad can pop up. You can add quotation marks around the word or phrase to make it a phrase match. This means your ad will only show if they type in the exact phrase that is in your quotation marks. IF you put a plus (+) between words it will make it so it has to have all of those words but they can be in any order and your ad will show up on their search. If you put brackets ([]) around your word it will be an exact match. This means it has to be that exact same word. These key word optimizations will help to make it so you ad only shows for people who really are interested in your site.
Landing Page
The landing page is also very important to the success of you site. Customers want to be taken directly to what they are looking for. If they are looking to buy shoes on sale and they click you shoes sale ad but are then taken to your regular shoe page, they will most likely click the back arrow and try another site. To be more effective you should link the ad to the page that is selling the shoes on sale.
Also speed has a big influence on how long a customer will stay on your site. IF your site has a lot of slow loading images, chances are the customer will not wait long enough for them to load, they will click back and move on to the next site. Depending on your audience, you may want to consider to loading time on mobile vs desktop screens. Optimize according to what your audience will be using most.
Another big turn off to a customer is poor design. If it is hard to find things within a site, the customer will likely click out and try a new site. If things are easy to find, they will be more likely to stay on your website and browse through different sections.
Google Analytics has a program to do A/B page testing. This means you can make two pages and test them to see what is more effective and will keep customers longer. While setting up this test, you can choose what percent of your audience will be a part of this experiment. This can help you to determine which layout is most effective.
Links:
Get More Traffic with Keywords
AdWords Optimization for Beginners
Landing Page Optimization
Google Analytics: Experiments