Before starting on a piece, you need to think about how you want it to sound. Often, I can put together an entire orchestral piece in my head, but noting it down can sound very different. This is why sheet music is often handy. I always make sure I know just what I want before I start. For The Palace, I wanted it to sound epic-orchestral, and very recognisable.
Once I have a good idea of what I need, then I start on the notation process. All of my music is MIDI, having no access to a live orchestra. The only exceptions may come later in time, when I may or may not start using instruments I have available to me. I first note down the songs with low-quality sound files in Fruity Loops 5, so that I don't use up too much CPU just getting the notes down. Once I have that, I then start adding in some higher-quality ones. For this, I use a program called East West Quantum Leap Symphonic Orchestra. This is an expensive piece of software with a bunch of live recorded orchestral instruments. Really handy!
Once I have this part done, the tunes are starting to sound good. Occasionally I have to make amendments. For example, in The Palace, I originally had the intro playing on a Spanish Guitar, but, having taught myself the intro on piano, I decided that would be a better way to go, since I love the sound of a piano.