First, you should never "guess" what people are searching. Use one of the keyword research tools available online to find out exactly what people are searching for - and how.
You can use the free trial version of - this is the one that I use myself and can recommend.
I would start there...
Another thing to consider is that you want your keywords to be as specific to your offer as possible. Dont use general keywords or general phrases... find phrases that people are actually using to search specifically for the type of thing you are offering through your ads. The more your Ad matches their search, the better your CTR.