OK. First things first ! You need right tools and I recommend to use 3M vinyl because 3M seems to have strong Adhesive and its pressure active so its easier to work with. Make sure you do it Dry.
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Tools
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There are few ways to finish your edges.
One is to use knifeless tape.
https://www.youtube.com/watch?v=8r8R...e_gdata_player
Watch the video.
Second is to hand cut the edges with knife. This one is very tricky . you need to make sure Blade is not scooping the paint instead of cutting only vinyl!
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Use nothing but olfa carbon blade. And make sure All edges are folded in and stays nice and smooth before cutting.
I will post the more process after I'm done with the BMW.