you should never buy shity tint,,but if you have some good tint then do it up..i did it with my gf's brother and other than a few things it was pretty good for our first time..
take off your panels
unhook everything and take your window out
you really gotta clean the windows
then you gotta mix soap with water around 85-15%
then you wet the window with your solution, no SOAK the window
then have a friend peel the tint while you spray the shit out of the tint, this insures that no dust gets attracted to it.
apply the tint to the window and set it in place
use a card or if you have one a squegie* to get the majority of the water out.
then get a hair dryer and get all of the air pockets out.
use your card again if nessisary (making sure you dont apply too much pressure and rip it)
dry again making sure there are no air pockets left
use the same method for the other window(s)
we did this and it came out pretty good for our first time. it was pre cut tint for his car so try and get that if your are doing it yourself..its not that expensive and really fun to do so do what you want but thats what everyone agrees with so its a good source.