I enjoy mashing up music before most of my shows... it's like cheating on a test almost. People love what you are playing, but have never heard it quite like how you are playing it.
Over the past few weeks I have had quite a few shows which have varied quite a bit so Mashup's have been second only to breathing in my life.
My current method:
1.) I get the key of the track (Mostly I cheat and use mixed in key (MIK) it gives me key and BPM)
2.) Then I drop the track that I want to mashup into LIVE Warp using the BPM Given by MIK as Ref I find the 1 beat set 1.1.1 there and make about 7 warp marks with the Metronome on
3.) Save the file
4.) Decide what this mashup is going to be for (pool party, dance club, grandma's 80th birthday) then find complementary genre and key'd song in my archives (warp those songs like in step 2)
5.) Then creativity happens... I start cutting pasting and adding just enough of my own flare to make it unique to my style. (I try to never spend more than an hour on each mashup)
I just felt it would be cool to talk about current methods and styles other people are using to Mashup tracks as this is one of the the best dirty pleasures of being a prod/dj its almost a guilty pleasure of mine