keyword research myths

I have been reading many guides here in regards to keyword research and some of them are really good and i apprechiate the people posting their valuable knowledge.

I expected reading all the guides would get me more familiar and confident with my keyword research however i just get more confused. One guide said to toraget search volumes of 1500 + another guide said to keep it under 300. One guide said any site in google under 1 million is good another siet said anything under 500 000 is good. I know these are just peoples personal methods and they are experts but as a newbie i want to pick a niche that is profitable and that over time i could dominate. Can anyone explain to me the best way/guide to go about doing keyword research?

Also im not sure about this because im a newbie so anyone please be harsh and enlighten me if im wrong but everyone preaches to keep sites under 500 000 and under 5000 in google however isnt the competition of the top sites just as important? I found long tail keywords with high search volumes and the first page of google are two ezine articles and the third site is a PR 2 site with 340 backlinks. I was thinking top page compeititon is just as important as numbers? Or am i just missing a piece of the puzzle? lol