Hey Juho,
Finnish people have such cool names 😀 .
Any tips? Just be you, you got asked for a reason. Someone believes that you can bring it. A little bit of stage fright is to be expected and actually helps create the adrenaline that will make you do even better. So welcome the feeling, it will soon pass once you got through the first few tracks and mixes.
Be sure to have promotional material with you, if you have any yet (don’t get all extra nervous if you don’t, just make it a to-do for your next gig). Dress to kill (but that is just personal). I am getting a bit tired of guys getting up behind a DJ booth and play dressed like they just rolled out of bed or straight out of their bedroom training session in old crumpled jeans and dito t-shirt. Personally I think there is nothing wrong with showind some respect for your (paying) customers and audience by spending a little extra time on your appearance.
I am not suggesting suit and tie (although that might not be such a bad idea for a wedding, depending on what part of the world you are in), but whatever it is, be sure it’s clean (goes for personal hygiene too, deodorant, hair, after-shave, beard trimmed if you have one) and not looking like you grabbed it out of the laundry hamper.
Hope that helps, but the biggest tip any of us can give you here is ENJOY! You’ll only have one first gig ever. Make sure it’s one to remember.
Greetinx.