See TintDude (http://www.tintdude.com/tint.html) for instructions, but bear in mind it is a pain the ar$e job to do. Practice on a window in your house first (trust me it helps).
Also, don't forget tinting the front doors or front windscreen are not allowed.
the hardest windows to do yourself are the boot window, and the rear 2 windows. and since those are really the only ones you can get away with its definitely worth paying a pro. I've never seen DIY window tints thats looked anywhere half decent.
You'll pay 150-200 quid, but its definitely worth paying the extra.
on a side note, i've taken off my door tints. It was surprisingly easy (once i borrowed my sisters hairdryer, lol), and the leftover glue bits only took about 30-40mins. Whole job was done in an hour for 2 windows.
Its made my rears look really light though
If i wasn't gonna sell it, i'd definitely take those off, and get limo dark ones put on.
Buzz
The champion of the Bravo 1.4
Owner of the Bravo 1.8