To tame a Megaloceros, I would try to tame an Argentavis and carry it to somewhere warm. Assuming you have plenty of Mejoberries from any berry collector, or even by hand, or you could have Dimorphodon kibble you can begin taming. I would suggest using a bola, because these guys like to run. With a few tranquil arrows to their head they would be out quick. These guys don't usually need much narcotics. The megaloceros is amazing at collecting thatch, and they have a bleed effect, which is great for pvp and killing dinos.
Easy tame, just use bolas, trap/protect it with spike walls, feed berries, and use narcotics/narco berries to keep torpor up. I play on a small tribes server and tamed a max level in less than an hour with 3x.
Deers are easy to tame because all you need is to find a good level deer and bola it and punch it out or tranq it or club it. And feed it meoberries. Also narcotics or narcoberries to help to stop it from waking up.