Finding targeted keywords is based on two important factors: the level of competition for that keyword or phrase and the popularity of that phrase.
1. First things first: decide what your major keywords and phrases are. This is fairly obvious so I think only a cursory mention will be adequate. Obviously if you have dog training products you need phrases to do with dog training products in your title and scattered liberally across your page. So far, so good.
2. Find keywords with the least competition. This is easy, just google words or phrases to do with your product (preferably phrases, they're more specific) and if it comes back with less than 1000 search results, consider the phrase relatively low in competition. Remember, less competition is a good thing.
3. Of course, even if a search term has less than ten results, it won't mean a thing if that phrase doesn't get any searches. A simple and effective way to determine which words and phrases DO get the most searches is via free word tracker programs like freekeywords.wordtracker.com/. Type in a keyword or phrase and it basically tells you how many search results that keyword/phrase gets each month on that particular search engine. So just to recap, you're looking for a phrase that generates few search results yet gets searched for a lot (over a hundred searches is good).
4. If you've hit a brick wall, get creative. Open a thesaurus and search for synonyms of the phrase or word you were thinking to use and, eventually, you'll hit a gold mine.
5. Once you've found a highly searched for term with low competition, you need to make it clickable, that is, attractive to the consumer. Here's where you need to do some thinking to make the title jump out. For instance, try making the title numerical; instead of "losing weight", try "4 easy steps to losing weight", it's just more snappy. There are lots of other ways to make a clickable title, adding shock value also works. It seems counter-intuitive but making the title insulting works wonders.
So there you have it, the tried and true method for finding keywords that will generate you a lot traffic and, hence, a lot of cash.