Introduction to Aerobatics

First of all, I want to explain some of the most important aspects of any aerobatic maneuver. These are:

Correct placement of maneuver
Most people confident in fast forward flight can execute aerobatics such as stall turns, loops and rolls without too much trouble. However, many aren't so successful at executing the manuver in a specified position such as right in front of them each and every time. Contest judges will deduct a large amount of marks for maneuvers that are not correctly placed.
You should aim to practise a maneuver until you are confident that you can execute the maneuver from any direction in any position.

Straight and level entry into maneuver
Many people (and I'm more guilty than most!) make a hash of the entry into a maneuver. Starting the maneuver whilst diving, climbing and/or flying sideways (damn that heading hold!). This is just about guaranteed to screw up the rest of the maneuver. It can also produce some very hairy moments too! An example of this is at the first competition of this year here in New Zealand (the first competition that I'd flown the Vigor in) I entered a roll a bit low and with the nose well down. The result was a high speed diving roll that had everyone's hearts in their mouths as the Vigor pulled out at about 10ft off the deck... That taught me a thing or two real quick!

Smooth and controlled execution of maneuver
Another big mistake (and once again, I'm as guilty as everyone else!) is that pilots are often in too much of a hurry to get the maneuver over and done with. One of the more common occurances of this is during the stall turn where people just lay into the rudder and hold it in until the heli has come around at max piroette speed. It looks a bit crazy in comparison to to a smooth controlled piroette which will just about always score more.
Take your time and slow down, the quality of your stunts will thank you for it.

Straight and level exit from maneuver
How you exit the maneuver is important as well. The helicopter must exit where you want it to, not where it wants to! Doing a roll is great, but if the helicopter is heading off in another direction when you exit, you won't score too highly!

These basic principles can be applied to any aerobatic maneuver. They are mainly concerned with FAI style flying, but many can be applied to 3D flying as well.