Linden S. Barclay
This is always a big question, and every author has their own answer to it. For me writer's block is often a symptom of other underlying problems, most commonly fatigue, either physical or emotional. Other times it's a symptom of having reached a saturation point with something, and needing to step away for a break. One thing I find helps is having more than one project current. If you get stuck on one, change to another for a time, whether that is a different novel, or short story... planning/outlining instead of writing. A change of activity, or a change of environment can help free the block. If the problem is fatigue, then a nap is the way to go - usually in quiet to give my mind a time and space to process those things that are crammed in there and likely causing the block.