For a great review look at SARAH's, it's mint.
Anyway, after reading painful reviews and even reading about some poor soul peeling each letter individually I wasn't sure what I was letting myself in for.................however.............if you take that square piece of sticky back plastic and use it properly it is so easy, tedious but easy none the less.
1. take your lettering sheet
2. peel the protective backing off
3. place square sheet with lettering face down so that the sticky side faces upward (on a hard flat surface)
4. take the extra square of blank sticky back plastic and peel the protective backing off
5. carefully place the whole sticky film and place over the lettering so all letters are covered
6. once you have stuck the clear plastic to your letters, carefully and s.l.o.w.l.y peel the plastic so the letters are stuck to the new piece of clear sticky plastic
7. take your lettering and place inside/on toilet seat (or wall like me) and place where desired.
8. this is the tedious part, fins a sharp knife or tweezers because you will need them.
9. place lettering where desired and rub all the letters so they stick firm.
10. Now very carefully and S.L.O.W.L.Y start to peel the clear plastic but ensure the lettering sticks to the surface you are putting it on. This is where the knife/tweezers come in because some of the letters will play silly buggers and stay stuck to the plastic so gently ease them off while peeling back the clear plastic. This took me a little while but once done, all your lettering will stay evenly spaced and remain undamaged.
I hope this helps at least one person, so be careful before you buy, then moan and whine that the product is rubbish, it's not, your just doing it wrong lol