Research is the perfect start, but once you have a deer in front of you, all the reading and videos you went through will be a foggy memory.
If you know someone who has butchered a deer before - ask for help. Set the expectation that you want to learn, and you don't just want them to do all the work. Hunters are almost always willing to share their knowledge. Doesn't hurt to supply some beer.
I second most of the things mentioned already: time, practice, sharp knife, patience - these are all key. Don't burn yourself out, take breaks. A sharp knife and a dull mind will end in disaster.
Two things I'll note that you may not see in your other research:
1) have a good, clean place to hang your deer while you break it down. I use a
hitch hoist, let's me hang the deer anywhere I can park a vehicle.
2) have a comfortable height countertop to cut on. Saw horses are usually a few inches on the short side - your back will be done before the butchering is done. Add a few boards to get to a height you can work at where you aren't hunched over and you'll make the whole process seem easier.