How to make a bike skin!

[macca 803]

i know this is annoying but can someone please tell me how to make a bike skin.. theres nothing on this site that explains clearly how to make skins or how to start a skin. i want to make a 2010 yzf250 skin but i dont have a template or wireframe for it. and i hav photoshop to do it on, just dont know where to start. if u know of any info that helps with bike skins please tell me. thanks.