There are actions that are fun to do, like recreation, seeing friends or taking a nap. However there are things that frankly suck but need to be done, how to do this?
As author Dr. David J. Schwartz points out in the Magic of Thinking Big, the first step should be mechanical. What he means here is do the motions that are needed to start the task. For example, need to do cardio, get your shoes on and go to the track or piece of equipment. Need to work on a paper, start writing the title and opening paragraph. Putting off a conversation? Start with an introduction email. Got reverse DB lunges (me on Wed), unrack the DBs.
Bottom line, do an action to start the needed task. It might not make it more enjoyable, but it will get you turned in the right direction, and motivation comes from progress.