There is no silver bullet, but here are a few tips I use.
1. The longer you wait, the harder it is to start. If you wait too long, even a simple task will feel impossible. It's like approaching women. Your anxiety will start out low but soar as time goes on if you don't act. So you must start immediately to get moving or you will eventually will be unable to act at all.
2. Break the task down into pieces.
3. Start with the easiest and most fun piece first to get some momentum. No matter how bad the task is, there is probably one piece of it you enjoy. Starting with that will take your mind of this "I hate this entire project" thought pattern.