I believe there is an article about bet sizing in the "Strategy Articles" section of this site.
The standard raise is usually 2.5 to 4 or 5 times the big blind, but it all depends on the table dynamics and what you are trying to accomplish. Preflop, you will want to observe typical raises and go from there. At one table you may need to raise 6BB to get anyone to fold, and at others you may be able to accomplish the same with a 3BB raise.
Postflop is an entirely different and more complex issue and completely depends on the situation. Generally speaking, bet around half the pot or more up to the full pot. Betting more than is in the pot is necessary sometimes (facing a short stack that would be pot committed if calling a standard raise, shoving over the top of an all-in to eliminate the weaker/drawing hands, etc), but in a standard hand it is not recommended. Read up and get to know pot odds
very well. It will help you to further adjust your bet sizing.
As you'll read many times around here, it depends