First of all, its best if you have time to practice with it before the wedding, so if you dont like the colour, or have any problems, there is time for it to fade - when is wedding?!
Best time to do this is evening, a few hours before you go to bed so you can waft around in loose clothes to let it dry and then sleep in it and let the tan develop (warning - it will probably mark the sheets and make them a bit smelly but it will wash off, dont worry).
Exfoliate all over first. Moisturise feet (soles too so you make sure you get right to the edges), knees, elbows and hands (and any other dry patches you might have) with some rich body lotion. Ensure rest of skin is properly dry.
Be careful of turning eyebrows and hairline orange (put a tiny bit of vaseline on them).
If you can, wear thin rubber gloves as some tans really cling to your palms and edges of nails, even if you wash them immediately after application.
Cover hair with showercap/towel and also protect/be careful of surrounding area where you are spraying - it will be a bugger if the spray gets in your white grout (I am assuming you will spray in the bathroom).
Spray away and rub in as necessary. Be a bit more generous with spray on lower back (be clear why in a minute).
Moisturise tops of feet, around ankles and knees and elbows again with a tiny bit of moisturiser.
Remove gloves, wipe inside of wrists over with wet (not dripping) soapy cotton wool pad
then pat the backs of your hands onto your lower back so they get a bit of a coating to blend in with arms.
Good luck !