Rear quarters are easy. I did mine myself, and they are "nearly perfect". Front windows, again, if you can take them out great, if not, they are very tricky. I tried myself and failed.
Rear Screen...........pain in the arse. Due to the curve, you need to know what you are doing. Mine was a right mess, and ended up having to pay for it to do done professionally, as I did with the front ones.
Also, the quality of the film is important. The one I used to do it myself was cheap, and you can tell, as it looks purple from the inside, but the professional one looks smoked.
IMO, pay to have it done if you want it to look decent.