Translation into notation

I'm 16 and a well developed performer. I have my guitar, bass, viola, violin, singing performance skills but I believe my true passion lies in compositions. Whether its for my band, a movie, a video game, or just to listen something about creating music sings to me. 

I can sight-read fluently in alto clef and treble clef and I'm working on my bass. 
What would you say helped you guys learn to translate ideas and fragments of sounds into a fully written out piece of music? 

How do I work on not overwhelming myself when I'm composing?

And lastly, how often should i be practicing specifically composition?

Thanks :)

I don't know how you've composed thusfar but I use the following system:

I have a musical notepad (a regular notepad in which I've added lines in between the college ruled paper to create a 5-line staff) for just jotting down ideas.

For sketching out those ideas in slightly more detail I use a 8 1/2 by 11 inch sized manuscript paper.

Then for the final draft/orchestration I have a larger notebook with up to 18-staves to a page.

But that's only if you write on paper.  I've heard of people using their cell phones to record themselves singing if they have an idea somewhere - then develop it at their computer once they get home.

5 hours ago, said.whattt said:

And lastly, how often should i be practicing specifically composition?

I don't know what stage of learning you're at and what style you want to compose in, but sometimes ignorance can be a strength when composing.  There are plenty of exercises you could do to become more fluent in any given style of music but I would also be wary of getting bogged down with doing too many exercises and not just letting yourself be freely creative.

Anyways - I hope some of that helps!

To get from your head to a score? Just experience and practice really. It takes time. But if you're good at sight reading you should be able to "reverse sight-read" - think of a tune and know how it'll look on paper/stave. Practice sight reading things from the style you'd like to compose in. Study scores or instances (such as game-tracks) of the sort you like, to learn how they work. Developing your own voice/style will come as you move on.

Some basic CPP theory helps because it'll give you a sense of how progressions work. Learn the basics of the piano where you can see chords actually laid out and experiment with changing them. As you develop an 'ear' you'll get to know how individual parts move around. (but as a personal opinion, don't get too bogged down with theory, its nomenclature, its rules - that's unless you want to approach composing as a technocrat! ..well, you'll always be involved technically to an extent but don't let it kill off your spontaneity. I dropped out of formal musical education because it was stripping composing of its creativity.)

Other than that - perform. You have a band. Compose for it. And always be self-critical. 

My tuppence-worth.