I guess it depends what makes you stop
- Parts of it are too hard given current experience. Perhaps an easier goal would help.
- It gets stuck because it wasn't well designed. No need to describe every details, but it can help to have a general outline, both functionally and technically.
- All the fun parts are done. Maybe try to focus on completing small parts one by one, instead of doing in 'random' order
- You came up with another, more attractive idea to work on. Keep in mind why it is that you want to finish one thing, instead of having fun doing a bunch of incomplete things. It's not necessarily a problem, but if it is, you will probably know why. So keep that goal in mind.
As a side note, the title of this topic really doesn't convey any information, it would help if you actually describe your problem or ask your question in the title.