Conserving energy during a race

stand when you have to; sit when you can. (note that this is directly opposite of the old-school "always stand")

let jumps, logs etc help lift you off the seat (if you can) you when you need to- saves the quads.

relax your arms, stretch them on smooth straights.

hydration system? if you drink while moving, make the mouth tube easy to get with your left hand (leaving the throttle/brake hand on the grip). if you drink at checks/pits mostly, make the mouth tube easy to get with your right hand (leaving your clutch hand free to hold it in). take small sips every 10-20 mins instead of huge gulps.

eat light but steady as you can during the race (believe or not- french fries/potato chips have lotsa potassium and sodium, along with simple carbs); drink fortified water (gatorade, pedialyte etc) but don't get bloated. a small piece of beef jerky provides a long burn but can cause water consumption so go easy.

if you're not pitting yourself, get off the bike and stretch/walk a bit.

I've never done a long-long race. I might have a pepsi or something at hour 8 (I don't use caffeine much).

have a change of gloves and goggles on standby. be mindful of your hands, if warm spots develop (pre-blisters, basically) put some kevlar glove liners on.

if you find yourself fading, maybe slow down some.

the race is won in the last minute, not the first.

Try to use your knees to steer more thereby relaxing the tension on your arms and hands.
Remember 12 hours is long time in the saddle so pace your self. If you can, soften the suspension a tad more than normal. It is ok to bottom out from time to time (I am assuming you are not doing table tops et al). Take a potassium table the night before and in the morning well before you ride. Try to slowly increase your water intake 24 hours before the race (pre-hydrate).
Most of all enjoy yourself and relax.

Short shift instead of high RPM.

remember to breathe