Recently I started a new sketchbook with a new sketchbook philosophy. Here's the idea: time in the sketchbook should be pure unadulterated fun. Michael Jordan couldn't get in the zone if he had to the ref the game at the same time.
John Cleese of Monty Python speaks heavily on this topic in this talk.
When you go to be creative there are two distinct modes, the open mode and the closed mode.
In the open mode the only rule is that you have fun. You enjoy it. You're not trying to make judgements on whether what you are making is good or bad.
Then go into the closed mode, the execution mode. This is where you edit and make judgements.
I suggest you play more in the open mode in your sketchbook. This doodle (above) is an example of experiments in the open mode.
You might just have more success and surprise yourself!
Happy open doodling everyone!