IMO- In My Opinion-

At least I think that's what it means.

Most of the time when you see that it REALLY means In My Opinion the ONLY way to do (whatever they were giving an opinion on) is my way which I am about to TELL you and you better do it MY way or you'll be doing it wrong.

Sometimes it's just an opinion.

Figuring out which is which is the fun part. Once you've been around for a while you'll have a better idea how it works.