Ok, the first thing is you must check the rules, now if possible. Many MMA fight rules don't allow throwing in the towel in the middle of a round. Also check whether head shots to the head are allowed or not, what locks etc are allowed. Also check how far round the ring/cage corners are allowed to go, it's usually only halfway round either side from your own corner, you could get your fightr penalised by going too far.
On the day of the fight your job is to 'nurse' your fighter so all he has to do is concentrate on fighting. Get his food sorted, his kit checked making sure his groin guard, gum shield,entry music, shorts and gloves are there. You will need stop watch, Vaseline, tape for gloves, bucket ( sponge too if he wants one) if heads shots allowed get an old fashioned ice bag and secure a supple of ice or borrow some boxing irons, I also take some cotton wool or lint pads to deal with cuts. Do not put water on cuts, it makes them bleed more. Very firm pressure on cut should stop bleeding then a dab of Vaseline (petroleum jelly if you don't know the trade name) Pro cut men have other things to stop bleeding but it may be illegal for where you are so I won't elaborate. Take a bottle of water and also a spray for water and a towel. Take a kick bag and some focus mutts.
Make sure you get to the venue on plenty of time, find out when the medical and the rules meeting are. His coach may do all this but you do it too. After the weigh in make sure he eats and is hydrated, keep him calm and focused. Get a programme and find out the order of fights and the approx time he's fighting and which corner he's fighting from and how to get from the changing room to that corner. If he has entrance music get it to the DJ/sound people marked with his name and corner plus what track. check how many rounds there are and how long they are.
The time between the weigh in. medicals etc and the time to warm up should be spent chilling, keeping his confidence up and with you looking after things.
Warm up, don't warm up too early, don't let him bang the pads hard, don't let him rehearse moves at this point, the warm up should be just that, warm the muscles up and a good stretch, some light pad work. this isn't the time to impress people with the power of your punches. check everything is comfotable, shorts, groin guard etc. He may want gum shield in them or wait until in the ring, whicher make sure you wet it first. check what he wants done between rounds, although make sure he has water. Some like to be towelled down, others like ice on back of neck. Sort all this out before you go in. It's whatever makes him fight better.
When they are ready for you a runner will come and tell you. then wait to be announced and for the music to reach the bit you want to walk out to, don't rush out, walk out with confidence. If ring, lift ropes for him to enter, falling flat on your face not a good look.
Normally before a fight we've worked out the words we will use to signal moves we may see coming or think he should do, this may be difficult for you if you have no MMA experience. However you still may see things he can't so watch very carefully so you can pass the info on. for exaple, his opponent may always drop a hand just before he kicks, may always kick with same leg that sort of thing.
In the ring before the fight starts, remove t shirts etc. The ref will check gun shield, groin guard, soles of feet and gloves. If your fighter needs his hands taped pm me and I'll go through it. The ref will also check for grease, water etc on the body however it's usually permitted to smear a small amount of Vaseline around the ears and over the eyebrows. If your fighter is nervous keep him facing away from the centre of the ring and looking only at you, this is the time you tell him very forcefully that this is what he's trained for, that the training is the hard bit and this is the pay off, the good bit. It is actually easier to fight! Make sure before fight starts that if he's had water it's not spilled on the canvas, check before rounds start each time otherwise ref gets peeved! At the bell start the stopwatch, let him know when he has a minute left and then 30 secs, an extra burst in the last 30 secs can win the round/fight.
During the fight make sure you behave well! Keep any advice short, he won't be able to hear much. Between rounds don't tell him anything other than is pertinent to his fight, he doesn't need to know anything about the crowd, don't tell him he's dong anything wrong word it so he doesn't lose confidence. You will have rehearsed in your head what you are doing between rounds so it should be realatively easy, place water etc exactly where you know you can put your hands on them.
'Throwing in the Towel' as I said check the rules, many MMA fights don't allow throwing in the towel as it's the ref's responsibliity to stop the fight if one fighter cannot intelligently defend him/herself and while many people argue that fights are stopped too soon most refs get it right. the ref will stop the fight to check any cut and will either send the fighter back to his corner to sort or get the doc in to check. whatever though it's unlikely that in an amateur fight you'd have very much to worry about with your fighter being hurt.
After the fight, win or lose, your fighter will need cooling down and rehydrated, watch too for adrenaline dump or just being miserable at losing! Keep them up if they are down, if they won you'll have to listen to the fight time and time again lol but hey that's fun! Hope this helps
Good luck!
If you have any questions pm if it's uregent ot just post I can always get more advice of others!
Good luck and please post the results!! 
