First make sure you are not online on our server. Next, just practice... imagine a bowling ball balancing on a toothpick. In the end, it's not about "what altitude" or "what speed", it's all about feel - you either become one with the coppi or not.
Other skills worth learning are:
Parking the choppi in mid-air, requiring no further stick or throttle input for at least 10 minutes (or until CAS gunner is out of ammo and needs to RTB)
Doing a barrel roll to avoid an incoming missile while high enough off the deck to recover and use the (new) downward/forward momentum to escape MANPAD range
Hovering over water high enough to not crash but low enough that passengers can get in
Hovering over an unlandable area low enough that passengers can safely load up or depart
Dropping a crate on a small building rooftop correctly the first time, everytime
Memorizing every AAA/SAM location on every map you play