If your wood is showing signs of burning or splintering as it moves through the saw, you probably need to sharpen your blade.
The Family Handyman on MSN

Cutting Baseboard Corners Made Simple

Use paint stirrers, popsicle sticks, or any other thin flat material that you can nail through to shim the baseboard against the wall and snug up the miter. Slide the popsicle stick behind the bottom ...