VHT Nite-shades FTW..... make sure its VHT! high quality stuff!

either way you do it i HIGHLY sugest wet sanding your lights smooth... remove any scratches, raised lettering before tinting either way. dont worry it will look alittle cloudy after sanding but just tint over the lights with them clean and your golden...... just let the spray tint dry well before touching it!
BUT BE WARNED!!!!!!!!!!! by tinting your taillights you are hindering others from seeing your brake lights as well durin gthe day! at night time its no problem BUT during the day the sun reflecting off the tint makes it really hard to see brake lights...
ive tinted, sanded, tinted sanded SEVERAL TIMES till i found the good VHT Nite-shades spray tint that lays down smooth and easy! and if you dont think they turned out good just sand the tint off with some 2K grit wet sandpaper and then with some simple fine rubbing compound or a nice wax to shine the taillights right up to make them just as good if not better than when you started since now they will be scratch free and shiny
ive had them done several times.....
and the lettering why it looks bad if you dont sand it off smooth before tinting!

just keep sanding till its all gone... helps if you spray paint around the area or something so you know when youve sanded them off.
start out with some thin coats and work your way darker till you think its right.. the more layers or thicker you paint the less light will shine thru! but remember if you tint to dark its only alittle sandpaper and about 1hour or less to sand it down all off with some 2K grit wet sandpaper. you can probably use 1K but i didnt want to risk any scratches to deep....
if you want to step it up to be SAFER for day time driving which i HIGHLY SUGEST... some extra lighting helps... i used some red superflux leds BUT i didnt like how it turned out so right now im rocken factory taillights again till i can buy enough leds to redue my taillight setup....

my new taillights will have abunch of flexled strips in the lower clear section. gonna use red and some yellow strips to keep it safe for daily driving! i baked the outter taillights apart to put these new led strips in. i thought about the inner taillights BUT they busted while trying to seperate so im gonna stick with just the outter taillights being lited.

thats just a TEST with one 9.5 blue led strip i had laying around...
heres a few videos i have of the few different types and darker layered tint...
http://ca.youtube.com/watch?v=6sogcMcvlLo
http://ca.youtube.com/watch?v=rppuXbR9jwo
just a few things for you to consider.....
ALSO another helpfull think is before tinting your taillights tint the back/side/edges first before tinting the main taillights.... what happens is light leaks in from the sides/corners between the body/taillight and during the day it makes it look like your edges are red... you can see how it is in this picture below.... see the far left of the lense corner/edge....
so turn the lights face down and spray the paint/tint around the sides to kinda go behind the lense. and if you get tint/paint on the exterior front of the lense just sand it off and then tint it.

kinda hard to describe i hope you understand what i was trying to say....