In some puzzles you'll find a lot of the mirrors are there just to help you find other mirrors, and aren't actually part of the final path you'll need to take. You don't have to reflect off every one.

The game often makes you use sliding mirrors twice in different positions: one to illuminate another mirror or gate switch you need, and another for the final path to the endpoint. Experiment with the sliding mirrors on a level and find how different positions help you reach different parts of the maze.

When directing your light beam through gaps in the maze, small changes in angle can make a surprising amount of difference. Cycle your light beam around and light up whatever you can.