Set practical goals for yourself in what you want to learn. Start small because you can always expand later on.
Create a game plan including resources and a schedule. Figure out how much time you have to dedicate to this self-learning project. Give yourself a few extra days for leeway and call them "catch up days." Often things take longer than planned or life throws curves at you.
Stay focused by meeting your daily goals and don't get discouraged if you don't meet your goals on some days.
Broaden your horizons by learning topics on the fringe of your interest level. This keeps your mind fresh and introduces you to areas of life you might not have realized you were interested in. Also, try to schedule "hands-on" self-learning--it's more interesting and you retain more information because it's more memorable.
Reward yourself for meeting goals when you follow your plan. It's important to keep the self-learning fun.
List the benefits of self-learning once you have achieved your first goal. This list reminds you of why you did it, and why you want to continue on as a self-learner.