Remember the best writing you can achieve is writing that isn't forced, writing that comes to you naturally, but that does not mean you let nature dictate when to write, how to write and how much to write. The more you write, the better you become and that is why I always emphasize the importance of never letting a day pass without writing anything. If it doesn't come naturally, your creativity may return when proof reading a second, a third or even the seventeenth time and overhaul what you had written.
Where do you write best from? Find out and maintain it for it may be the only solution to your constant writer's block!