Don’t bite off more than you can chew. Things can get very daunting very quickly if you don’t break things down into their component parts and set yourself small tasks. You should always try to have a good sense of the whole, but, as you can’t write the whole thing in one sitting, once you have that sense, just work on small tasks for a while.
2)Don’t throw sketches away, even the things that didn’t work. Revisit them. You may well find with a fresh perspective that there’s something there. If you don’t find that, try to understand why something doesn’t work. That can be a valuable lesson. Go back and look at your initial sketches. I’ve lost count of the amount of times that I’ve gone back to look at my initial sketch only to find some compositional nugget scrawled on the corner of a page that has become the key that unlocks the piece.
3)This is a little thing, but something that I find quite useful: When you finish for the day, leave a little something undone. Nothing that requires a half hour of trying to figure out what you were doing, but something that you need to fix the next day. That way you’ll start up working again more easily.
The fifth and final thing is the use of external creativity tools, something that gets the creative juices flowing, beyond the musical sphere. Some composers read, some go to art galleries, some watch movies, some go for long walks. I suppose I do my combination of all of those but there are things to help that you can find from the comfort of your own work desk. One thing that a friend sent to me recently I haven’t really used, but I’ll pass it on as something that might be quite useful: Brain Eno and Peter Schmidt’s “Oblique Strategies”. They started life as cards in a pack for use when ideas were at a premium in the studio. You can buy a new edition of the cards, but you can also find them online, here for example: http://www.joshharrison.net/oblique-strategies/
That’s pretty much it. The creative process is a strange thing and so many things happen along to way to give the impression of randomness but you can control some of the variables. Every composer has his or her own way of working, but most composers that I’ve spoken to do some variation of the above. There will always be emotional highs and lows along the way, just remember that everyone goes through this. That’s part and parcel of the creative process and you can mitigate some of it by trying some of the methods above. If you’re in the throws of creative depression and you want to make yourself feel better, just take a look at Beethoven’s sketches. If trial and error and frustration are good enough for Beethoven, they’re good enough for me.