The first thing you have to do is keyword research. Go to the Google Keyword tool... search for this in Google to find it if you don't know how.
Now type in words related to your content. Then pick the top 3 most searched and related terms.
Next type them directly into Google. Look to the right and make sure there are at least 4 advertisers spending on the keyword phrase. If not then you'll need to find 3 phrases where they do spend.
Once you have that it's very important that at least one of these phrases occurs in your title Tag. You should also try to incorporate a variation of the other 2 phrases into the title tag. Use plural forms like this.
Cars are a huge investment - Here is what to look for in your next Car purchase.
Note: cars - car 2 different keywords.
Try also to incorporate similar words - car, automobile, vehicle, etc.
Once you have a really good title it's time to "seed" the keywords in your article.
On a PC use control F to search for your keywords to make sure they are in your article. If they are not, then PUT them in your article. And make them prominent. This means more towards the top of the page, the first part of a sentence, etc.
Bold them on occasion, underline them for emphasis. Put them in your sub titles.
It's these tactics which help Google determine what your article is about. And if you do this the content will match the ads.
I run a large network of sites. I've been doing Adsense since 2003 when it first came out. I've written 10.000's of pages of content. And this works. And this will absolutely put more money in your pocket. It's a little extra work, but without it you are flying blind.