Check your corners before you cut your miters.

I'm installing baseboards in that room, and where the boards meet in the corner, you cut the end of the boards at matching angles so that there is little to no gap at the joint. A lot of people assume that the corners in their house are 90 degrees, so they cut 45's and then when they install the boards, there is a horrible gap because none of the corners are true 90's. In the video, you can see that my corners are more than 90 degrees, or they are open, as we say in the trades. So, if I cut them at 45, they would meet at the back, but not meet in the front.