Finding keywords from the Google Search...

I'm no keyword expert - on the path of learning all the time, though. But I'll throw in my 2 cents on your question.

When you type a word into Google's home page in the search box, that list of suggestions for related phrases that drop down is called Google Suggest. I find it a helpful tool in uncovering more low competition keywords that I might not find if I'd used only Google's Keyword tool.

Take your diet pills example. When you type it into Google's home page, Google Suggest gives you:

diet pills that work
diet pills that actually work
diet pills for women
diet pills that work fast

Google's Keywords Tool doesn't return the result "diet pills that work". It gives you "diet pill that works". You might not have found this other keyword possibility had you not used Google Suggest.

Keeping that in mind - that Google's Keyword Tool won't return every possible option when you enter a main keyword, I use Google Suggest to give me ideas of phrases I can type into the keyword tool, forcing Google to cough up more low competition phrases by going through the alphabet letter by letter to find more phrases.

So, for diet pills, I'd type "diet pills a" into Google's search box and see what came up with the letter A. Diet pills appetite suppressants comes up. Gives me an idea to check for keywords related to "appetite suppressant" in the keyword tool.

So on through the alphabet until I dig up keywords that meet requirements of decent search volume and low competition.

Maybe it's a lot of manual work, but I have a number of automated, paid keyword tools and sometimes I feel like I don't have enough to work with until I make Google give me more. Just when you think a niche might be all tapped out, you can find some nice keywords that were hiding away because people spent their time researching only the main keyword phrase in Google and didn't really dig down deep, as they say.

My little trick anyway.