You have to realise if you're not focused on one project your mind is going to be scattered everywhere and you'll end up with half assed products or incomplete projects. I made this mistake when i was trying to start something like 3 companies at the same time when i was 15/16, i wanted to do it all. You just can't.
For example if you had a series of essays to do in a certain amount of time, they'd all probably be mediocre or incomplete. Yet, if you had to do one essay in the same amount of time that one essay would be pretty impressive, you'd have time to proof read, spell check, change areas etc...
Pretty poor example but you get the idea.
Find one and stay focused on it.
When the idea becomes no longer fun get some feedback, nothings more motivational than feedback. There's going to periods were you just can't be bothered or were it tires you out and the next task/step is soo complex you procrastinate for weeks, you have to identify this and the fact that it happens and push forward.
On thing i do, it's pretty weird, start with really small tasks and build up til' you're in a productive state. (do the dishes, reply to emails, make breakfast lol) When it comes to the hard part (opening up the code editor and getting started) what i do is kinda' go consciously unconscious, you phase out everything, the task, every thought in your head (you might even go light headed), complete yet forced zen and just start coding, when you "regain consciousness" you'll have already started the task and it will be less of a mountain.
And prioritise.
I'm currently at university, in my first year, working on my new start up. It's more important than university to me, i haven't been a class all term and only about 2/3 lectures this term because i'd rather be designing/programming. My priorities are with my idea not with this degree, i have a load of other ideas and what i'll learn from this start up with help me with the others later on.
Just shelve the ok ideas and push forward with that one idea you love the most.
D