i guess everone has a different technique. these days i just jam around and some nice riffs appear. but i think this is mostly because of having some nice gear which inspires me.
i'll usually start with a low E palm mute playing 1/16ths, and then grab some random power chord, and with a bit of luck something will flow.
in the 'old days', when i had a more punk attitude, i just used rubbish gear for political reasons and it was harder to come up with something good.
i dont know what style of music you make, and you're obviously a pretty experienced player (much better than me probably). but buying the first six black sabbath albums and practising the riffs on those gave me an excellent start for most styles. then you i started to analyse the riffs - what worked in them and why, starting to bring in some of my own ideas. iommi plays in quite distinctive style, so learning some more progressions from other of your favourite bands in a similar way and mixing it all up is bound to lead to some good results. playing around with single notes and different chord inversions might give some nice stuff.
looking at sabbath some more. its not just the individual riffs iommi plays, but how the band mixes them up in the context of a song. sabbath have some really good arrangements, and i always learn stuff from listening.
i honestly think that the drums are the most important instrument in any music, much more important than guitar or vocals. it might be a good idea to work with a drummer and jam around.
also, i get alot of inspiration from dubstep and drum'n'bass. the synth riffs in acid house and rave music rock too. happy hardcore tunes often have excellent arrangements as well.