Do something related but trivial to get yourself into it. Momentum is the key. You're at a stand still. Pick the easiest or most interesting part related to the project and start on that. Even if it doesn't really make sense to do that first. Anything to get the ball rolling. Once the ball is rolling I tend to tackle the scariest part first. Whatever I'm not sure how to solve yet.

Visualizing the end product can work very well too. Create a sketch or non-functional version of what you're building, just to see what the finished product will look like.

If I was creating Google I'd make a really dead simple app that let you enter a query and returned 10 crappy links. Just to make the work tangible. This lets your brain easily grab onto what success would look like (e.g. 10 highly relevant links vs 10 crappy links).