I usually start by just jamming on the guitar until I come up with an interesting idea. Staying away from the guitar for several days always seems to spur the creative juices. I can usually come up with a suitable idea in about 5-10 minutes. I work up a rough outline of the song, being sure to leave a few 'holes' for spontinaety.
Then I record into SoundEdit 16 in stereo with my Apple PlainTalk mic plugged into my 7500. I can usually lay down the track in 1 or two takes, any more than that and I usually try something else. Keeping my music spontaneous is very important as I can't stand boring, stilted music.
I might then add more instruments such as bass or harmonica after importing the file into ProTools. Adding a touch of delay or reverb brings out the instruments and makes them sound more 'live'. If no other instruments are needed, I'll leave the track for a day then mix it the next day. Waiting is always a good idea, sometimes I don't even like the song the next day!
If the track is an electric blues song, I usually write it then map out the drums on the drum machine which can often take up to an hour. Then I lay down the drums first, then the guitar, bass and other instruments. I use Reason for my MIDI recording and save the track as an AIFF, then import that into ProTools, allowing 6 more live tracks to be added.
The drums usually come first, courtesy of Reason software. You can't add the drums later but you can always remove them if needed. Then I come up with a keyboard or guitar idea and add instruments as I go. If it's a MIDI instrument, Reason is the software of choice, if not, I'll record into ProTools. I have several plug ins such as reverb, delay, flange, etc for special effects, adding them sparingly during the mix.
These songs are almost always improvised. I'll get a basic drum pattern then add keyboard layers of 3 or more tracks. This is done rather quickly, usually in 15-30 minutes. All my ambient songs are recorded with Reason, allowing me to go back later and remove or duplicate segments very quickly. Reason also allows you to import 'loops' of sounds that you can download off the net or make yourself with Recycle, an app that records loops. I can typically record 2 songs in about an hour this way, including the final mix. Doing the same thing with my old tape recorder would have been impossible, plus they would be analog and not digital.
You can achieve some really nice effects with Reason's built in synthesizers and effects, often using up to 6 or 8 synths at once! Reason's interfaqce allows you to customize each bar or music, duplicate huge segments and doubling them with another instrument, even delete segments and bars or replace them with other instruments or samples, giving me complete control over every aspect of the recording.