I've always written instrumental in my head, but it is only in the last few years that I've really been able to record it as I imagine it; the main factor being the multitrack recorder so I didn't have to play everything live at once, though some parts were (and are) sequenced.
Recently, I tend to work by getting a group of sounds that work well together and then doing a mixture of improvisation, melody/bass line riffs I haven't used and evolution happens. Most pieces have a plan/structure before I start, e.g. "Exsistence" is pre-birth, birth to youth and then adulthood before death - whether you can pick that up from the music is a moot point!
Working with a guitarist in 2007 I re-did some of my older songs that needed more "oomph" and/or aggression, since then I've been trawling a deep sea of more rowdy instrumentals. Do not assume that sounds that are like guitar are said instrument! A Roland JD-800 provides most of the lead lines on current work, but some acoustic and electric guitar is used also. I've played bass guitar for a long time, but will never be a good guitarist; haven't got the patience to practice my chords for a start. Two of the newer tracks, "Fuldrive" and "Mjtiad" can be heard at the myspace link below.
Tasters of my 4 track CD are on my Myspace page - www.myspace.com/patternsoflife2
My iTunes page is
http://phobos.apple.com/WebObjects/MZStore.woa/wa/viewAlbum?playListId=203653221
It is also on the Real Napster, you will need to search for Patterns of Life and I'm first on the list! - www.napster.com. www.napster.co.ukBuy the CD in North America -

You can even get ringtones.
Other sites to download my MP3s....
The Music is Here....
Bitmunk.
Tradebit
Payplay.
Great Indie stuff.