Guaging and Blocking are probably the key to sanctification when it comes to knitting. I'm still really bad with taking guages, but I feel blocking is...just absolutely necessary.
A simple stockinette hat may not show as surprising results, but still will even out the stitches. I first didn't know much about blocking, and all I knew was "steam your finished project with your steam iron. Just steam. Don't press". Steaming and misting are the two other kinds of blocking, and you should decide which method to take depending on the fabric you're using, but I prefer dunking the finished projects into the water and leaving it for 30 mins, then ring it gently and shape it, then let it dry.
Blocking shows its power for lace project the most, I think. When you first finish a lace project, honestly---it looks kinda pathetic.
Edges curled up, the k2togs and stuff are kinda bunched up, yarn over-s are kinda there and not there.....but when you block it, this
Transforms into this.
so mark my words, blocking is, like many people say, pretty important. So do it! ;P