Practice.
I guess Maxx might have a proper guide written down, but basically if you were to pretend that you had three feet for a second, you would be able to press the brake fully and still blip the throttle as you press the clutch in so that the revs matched the gear speed as you let the clutch back up. All whilst staying on the brakes.
All you need to work out (which is easy when sitting here, but harder when in the car admittedly) is when to roll your foot over to blip the throttle whist NOT pressing harder on the middle pedal.
Most people use the ball of their foot on the brakes. If they are smallish (size 6 or less) they tend to need to swivel their whole foot over so their heel pushes down on the bottom of the accelerator - in other words they almost have their right foot pointing towards their left foot - if they are larger proportioned (no sniggering at the back !!) like myself then I simply "tip" my right side of my foot over towards the accelerator and press down a bit and hey presto it works !!!
I have been doing this for 15 years though, and I do it in most the vehicles I drive at least 10 times a day - usually the van, usually down country lanes for a mad 5 minutes !!!

Hence why i say PRACTICE !!!!
The only other thing I have found is that I get the revs wrong about 1 in 10 blips whilst driving flat out, and 1 in 20 results in a jerk on the brakes. When doing this technique at relaxed speeds I find this goes up alot to more like 1 in 5 and 1 in 8. I dont know why - lack of concentration probably !! - but its worth noting !!!
Hope this helps,
J.