Build the discipline of action.
When you get the motivation, the action will be a natural step forward.
Every time you avoid facing a problem, think that that is only one of the ways of responding to it.
It depends on you what you choose to do, but only by confronting the obstacle, by acting can you overcome it. Force yourself to take action.
When you cannot motivate yourself to do something, remind yourself how fast and creative you are close to the deadline or in urgent situations.
As you can see external factors can effectively motivate you. When they are absent, look for internal incentives.