Get Perfect Miter Saw Cuts // How To
Using a miter saw that does not cut square is a frustrating experience. The principles I show in this video apply to most miter saws.
However, the method of making the adjusts on your saw may be different, see your owners manual if you do not know how.
To adjust the blade square to the fence you loosen the detent plate or fence (depending on your saw) and then use whatever square you have (even a piece of paper can work in a pinch) to adjust the movable piece until it is square, and then tighten it down.
Adjusting the bevel is essentially the same, except your reference your square off the blade and table, instead of the fence.
After everything is adjusted, make a test cut to verify that you are square. I show a neat trick in the video for telling if your saw is cutting square. If you are really concerned with precision though, you can use the 5 cut method.