+2 on the hairdryer (not a heat gun!). Leave it in the sun first to heat the mass of the part to be stripped, else it will take longer to soften.
Pressure sensitive film adhesives like decals shear best at around 30 degrees, so once you get it started, rather pulling it back on itself past 90 degrees like most folks do, keep the leading edge behind the shear-line. This helps the adhesive stick to the decal, instead of being left behind on your bike.
If adhesive is left behind, I wet a paper towel with Varsol and drape it on the area, leave it a few minutes, and it dissolves the adhesive. Then clean the oily Varsol residue off with isopropyl alcohol (rubbing alcohol).