For me the keys are: prioritize, note every ideas, talk about it to everybody, take breaks from it when needed, never give up.
Prioritize: Pick your principal features out of everything else. Build them up so you have a fully functional game. Then do it again for the rest of the features/tasks.
Note every ideas: Today's ideas are tomorrow's updates. You never know when you'll need this idea. I answer my own questions every day just by reading my past notes.
Talk about it to everybody: The more you talk about it, the more people will ask about it and the more motivation you will build describing the game, inspiring you new ideas, getting feedback and sometimes people even has good ideas to use!
Take breaks from it: I personally try to get two days breaks every time I feel like it's needed. I spend those days playing other games, working on other projects, freelancing, etc.
Never give up: This is the hardest part. It's easy to get an idea, it's easy to build a prototype, it's easy to start development and it's also easy to draw basic arts. But it's harder to type thousands of lines of code, draw hundreds of sprites and animations and stay connected with the community all the way up to release. I love to think about the day my game will be on Steam, I love to dream about people reviewing it, receiving plenty of emails from people, etc. I always think about the people, how happy I will make them if my game is good and fun.
I think all I want with this job is to entertain people and make them happier with their lives. And this is what you should always keep in mind.
EDIT: About arts, I always hated them. But one day I started drawing them because I had no other choice at the moment and found myself loving to draw them. I'm not very good at it but I always improve myself. I think doing it a little every day is the key. (I use an iPad app called "Sprite Something" which is AWESOME and I can draw everywhere and whenever I have a rush of ideas.)
I hope this can help somebody else. Sometimes doing it all on your own is tough, but very rewarding.
