#1 Create a list with all possible keywords that fit to your product, service or whatever you are promoting. The more words you come up with, the more chances you get of finding the niche keyword which brings me to point 2

#2 Niche Keywords. Drill down deep into the word, expand on it. For example, if you are promoting affiliate products related to mothballs. Instead of just mothballs you can use mothballs for sale, mothballs for sale in uk, mothballs on the cheap , discount mothball etc The possibilities are quite huge. Use a combination of misspellings, adjectives and country locations.

#3 Make use of excluding keywords. If you are promoting a particular product say an ebook on making mothballs and it is sold for $100 dollars. You bided on the keyword blue mothballs. People searching for the term free blue mothballs would see your ad thus making it "clickable" and lowering its Click Through Rate. If you add a -free it would eliminate unwanted advertising costs.

#4 I usually choose NOT to advertise on content opting purely for search as they are more targeted and is of higher quality. BUT if I am targeting a highly competitive area where ads are like $0.80 per click, I would turn on advertising for content while disabling adwords for searching(lowering bid price). I would have total control over costs while having traffic extremely cheap.