Start slow finish hard.
If its buddy's first fight, chances are he's going to swing for the fences and you're going to think "this guys too strong, too fast , holy fuck!' weather the storm, conserve energy , then when he gases after a couple of mins, fuck him up.
You will feel heavy, like somethings wrong. You'll think that maybe you got sick from the weight cut. maybe you trained too hard and you should have take more days off before the fight. when you walk out from the dark venue into the ring your eyes will feel strange and you'll be super focused on every movment or you'll feel like your outside of your body and its happening to somebody else. Your opponent will probably look bigger that you though he would, you'll wish you had the skinnier guy from weigh-in. the gloves will feel weird and stiff. you'll probably be thinking you should have taken another piss before you got your hands wrapped.
Is normal!
Have fun!