If you've done them on a SIM they're not that different in reality (for something simplish like a loop), certainly for your 1st few though make sure you're absolutely comfortable with how the planes lined up before starting the loop and that the wings are level, if anything's going to get you tied up it'll be going in with the wings line off before you start and if you're not happy leave it, go around and start lining up again until you are comfortable !!!
Don't know what plane you're flying but one of the learning ones I had I'd just dip the nose slightly to build speed as the plane wasn't very powerful and then holding full throttle pull up into the loop until you get to the top and then as I was going over easing almost to idle as I was heading back down and then slowly increasing throttle as I came back to level flight.
One thing to remember when you think you're high enough to give it a try then go another 50 / 100 feet up and then do it, it's not a problem making a mistake as long as you have enough time to recover from it.
Good luck but once you've done one you'll quickly be back to do another !!!!!!!!!