if you are trying to build a habit out of something you enjoy doing, but still something you have difficulty getting yourself to do, set an extremely small daily goal.
if you want to write, write one sentence every day at same time. if you want to play music, play one note every day at the same time. by setting the goal low and doing it daily, you will find that on most days you do more than that one sentence or one note.
creating the habit actually exposes how much you love doing the thing. i'd suggest restricting yourself to this little bit for like a week straight just so you can build the habit. by the end of that week you will be bursting with a desire to do more than that one sentence or one note.
this also means that later, once the habit is implemented in your life, if you have an off-day where you really don't have the inspiration, all you have to do is write one sentence or play one note. i think the trouble with building habits is the pressure to upkeep them. it's so hard to start because you're not just initiating an activity for your day, you're trying to initiate it for the rest of your life. but if you set the goal small you will exceed it, and the pressure will fade.