As Remal said, hair dryer and try to keep it constantly moving to avoid damaging the paint. If you use a heat gun, keep it moving constantly even more or you'll be forking out for a new paint job or fairing Fishing line also helps, heat it up and use the fishing line like dental floss to cut through the glue. Then get some sort of solvent that won't damage the paintwork to lift the remaining glue.
+1 for the hairdryer..... It's about the only use I have for one now, if it leaves lots of sticky glue then you can use some brake cleaner or even petrol to remove, but always polish area after to remove any residue....
Removed an old one from the side of the speedo where it had a gear indicator fitted. A bit of petrol and a scrape off with your nail, got it down to a film and it came off with another rub with a bit of petrol.
This is an extremely tricky exercise and the last thing you want is to damage paint work which could result in £££££'s to repair. I would practice first, its what i did with great success.. First try sticking the 3m mounts to your arse, then slowly pull them off without causing pain or pubic hair loss, (ok a little pain can be fun). If you can master this move onto your testicles, trust me it takes time and patients but worth the effort.. I don't use 3m mounts on my bike anymore but still by a pack of 6 every now and then for practice of course P.S The hairdryer can still be used for many other activities but thats another story....