If male, make sure Daddy is at least a Brig and owns half of Yorkshire. Be sure to wear hunter wellies, shirt, chinos, blazer and old school tie. Speak in a loud, braying voice and constantly tell everyone that being in the OTC is the same as being in the real Army, especially since you have a scholarship gained from a few strings being pulled when you were sixteen and slightly less of an arrogant bell-end than you are now. Go skiing every winter, and summer in France. Make sure all the females are aware of how good you look in combats, especially if you've somehow blagged your way on to a PTI's course/TA P Coy and can swan around looking speshul. Talk loudly about blood grooves on bayonets and how you don't really want to kill anyone, but it's the job man.
If female, smile, giggle, flutter eyelashes at training staff and become very good at noshing off the latter and the former, apply cam cream like makeup, whine about carrying anything more in your daysack than cosmo and a pair of hair straighteners, be given a firearm only under very controlled, highly supervised circumstances, live rounds even more rarely. Make the most unfit male biff look like Usain Bolt.
Both must be sure to put 'British Army' under 'employment' on facebook, and have token 'warry' photo as profile picture. Said profile picture usually taken seconds before the C/Sgt who should really know better but is still banging the female unteroffizers screams blue murder at you for making a safety error that in the real world would probably end up in you gunning down half your platoon, but luckily since your gas parts are irretrievably rusted to buggery, merely results in a soft click, while you mutter under your breath about Daddy's shotguns never being this crap.
Did I miss anything?