I do this a lot. That is, I cut 24 bevels on 6 squares of wood.
The first trick is get your blade set at a 45 degree angle. Since I started using a digital level (Wixie Digit) it has made the task much easier. Otherwise, you would need to make repeated cuts on scrap until you get your angle. (Two pieces placed bevel to bevel will form a right angle that you can check with a try-square.)
The next trick is to use a dedicated sled with the slot cut at 45 degrees to the saw table top. It doesn't have to be a full size sled unless you are making large cubes. My sled also has lever-clamp and an adjustable stop (held in position by the two wing-nuts). It's hard to see the piece under the clamp, but it's there. Notice I have stop block clamped into the saw slot to prevent overrun and the blade guard behind the sled fence. The blade has not been lowered, yet, since it was raised to set the tilt angle.
Gives me perfect 45 degree beveled pieces every time.
Then I glue the pieces together using yellow glue and clamp with rubber bands.