How do you choose keywords



Basically keywords can be classified into many categories, long, short, regional,,, if you are targeting the users in a particular region you should use regional keywords, if you are targeting world wide,, then you should go for the long, if the competition is not heavy you can move for the short. the details regarding the competition can be analyzed with the help of keyword analysis tools like google ad words, webmaster tool and many
 
common sense + research + PPC

Common sense is not really meaningful to someone asking the question, like OP. It takes hard work and empathy to cultivate "common sense."

That said, use common sense. This would mean going to where your customers/visitors are on- and offline: forums, blogs, etc. Listen to their problems, see what they're talking about. Use those keywords + GAKT for search volume to find your winners.
 
You'll want to think about who is your target audience, and what the primary focus of your website will be. Need help on this one? Read my article titled Understanding Your Audience.
Jot down a list of words and phrases that you think people might type into search engines when looking for your site. Don't worry about being perfect: just be creative. This might be a good time to review how to brainstorm for keywords and phrases.
 
Agree with global geek regarding the need to ge tin the minds of your target audience. Assuming this is for a site that will ultimately be selling something, you want to make sure to focus on "buying" keywords instead of "informational"
 
Depends what you want to use them for, PPC keywords are picked more on ROI, long term keywords I want to rank naturally for I go for more medium/high competition and I dig out as many long tail low quality (talking 1000s, maybe even 10k+) for an autoblog
 
Keywords and phrases should be highly specific and relevant to your business. Google rewards relevance. It’s not just about paying to get to the top of the list. So your keywords should tie in directly with your ad copy and your website. When someone types your keywords into Google, they should be looking for a business exactly like yours. As a result, those people that click on your ad will already be predisposed towards buying from you.