How do you find valuable keywords?

Just want to know whats the best way of finding a keyword to focus on seo marketing.

What I actually do is I is think of a niche i want to go for, and just type in a word in a keyword tool relating to that niche. Sometimes I type in the product name, or 'how to' or 'where to buy' or 'what to purchase' and then a list of random phrases would be found, as I assume pple who type that are more likely to buy stuff.

Then the hard part for me is finding which phrase I should go for. I have been told that you should go for atleast 1000 searches a month and under 10000 for your competition, but not too sure if thats correct

most times I find that there are too much competition for my niche, so I just move on and pick a random keyword of the top of my head hoping for the best.

Is this how you guys do it?

first of all, the seo marketing niche is pretty competitive to begin with but not unworkable. i would definitely focus on the long tail keywords. sticking with keywords that have a good number of monthly searches and low competition is a good rule of thumb. it just depends on how fast you want to get ranked in the SERPs. just remember nothing's set in stone. testing and tweaking is key to finding the best keywords for any campaign.