I usually use Google for my searches. How I search depends on what I need. Sometimes, I just do a general search with only one term. But, if I need to hone in to something specific, I will string a few keywords together to get what I really need without having to sift through pages of search results.
I use whatever I have in front of me. Sometimes Google, sometimes Yahoo. I start with a general search. If the first page doesn't give me what I want, I add more keywords to the search bar until I get what I am looking for on the first page. I don't like sifting through pages either.
While selecting the keywords or key phrases i usually research on my competitive web sites and use their meta tags to find similar key phrases using Google Adwords tool. Optimizing the keywords is very much important, because you are optimizing them for search engines as well as for people who are gonna use the search engine.
I use Google, Yahoo and MSN search. Another way to optimize your site for better keyword results also comes from your own site content - especially putting the keywords in the metatag of your site's HTML code.
I usually use Google and I start with a general 3-7 word search. If I am looking for something more detailed, I start using full sentences. I usually just look at the little descriptions from google to see if I need the information from it.
I select my keywords based on the product I want to promote. Then I'll search out my competitors and see what they've optimized for. Then I'll aim at doing better than those individual pages.