well first of all is it a decal or an actual sticker? if its a very big sticker you have to be careful, also try and put the sticker on a fairly flat part of your helmet. i like to work my way left to right and just smooth it out. if its a decal, the clear paper can wrinkle a bit, just as long as the actual decal doesnt wrinkle. its hard to explain, but youll get the hang of it

Thanks, it is a die cut sticker

if you lay the sticker on the helmet without taking the backing off and blow hot air on it from a hair dryer it should shrink it a little bit and help form it to the surface. Then apply it as you would normally.

Wherever there's a crease, , make a small cut with a knife of scissors, and layer one piece over the other. It will be a lot smoother and better looking than just smashing down all the bumps.

There are a couple of different techniques. But generally the best way is to use a heat gun or blow dryer. Get a part of the stick on the helmet, either one end or the middle. From there heat up the part not touching the helmet yet and stretch it a little. Keep working it on there slowly. It probably won't be perfect especially the first time but with time it'll get there.

I actually find it a ton easier just to cut the sticker in 3 pieces and put each on one at a time