Lots of interesting things said on here so far. Most of them good, some of them pretty general wives tales in my opinion.
First and most important to me is to find a bow that fits you and is comfortable for you to shoot. Just like a gun if you don't enjoy shooting your bow you won't practice with it enough to become a competent shooter. That doesn't mean it has to be a new bow, or even an expensive bow. Bear, Martin, etc. make some nice entry line bows. Or you can choose to look for a used flagship bow, or go full out and buy an expensive Hoyt Carbon bow. Whatever floats your boat. BUT BEFORE YOU DO THAT go to a real pro-shop and get your draw length measured. A lot of people shoot draw lengths that don't fit them (usually too long) and they'll never be consistent. I would suggest you consider buying your bow at the pro-shop. That said if you're looking to pick up a used bow just be honest with them about that. No pro-shop wants to have you shoot 2 dozen of their bows until you find one you like only for you to go and buy it on the internet. If you're going to buy used have them measure your draw length, tell them because it's your first bow you're going to dip your toe into the used market, and then buy as many accessories as you can from them. Pay them to set up your bow, etc. Which leads us to...
Once your bow is purchased then you can begin the process of outfitting and tuning it. You can spend a lot on sights, quivers, rests, stabilizers, etc. but you don't have to. There are enough quality drop away rest options out there today that I would recommend that. Get a quailty wrist-strap release. Scott, SpotHogg, I shoot a Tru-Fire bulldog. Lots of good options but they're going to run you $75-110 probably. For your first year you can scrimp on sights, stabilizers and quiver in my mind. Find a decent 3 pin sight, something like a TruGlo that won't break the bank and grab it. Stabilizer and quiver can be had pretty cheap. Have your pro-shop install your rest, install a D-Loop (<--where you'll attach your release to the string) and pay them to help tune your bow (at least paper tune it after the rest installation). Buy your arrows from the pro-shop too. GoldTip, Carbon Express and Easton are the big 3 and their price will be pretty consistent no matter where you buy. They can cut your arrows on site, install nocks, spin tune, etc. I prefer a heavier arrow but I'm a decent sized guy shooting long arrows at relatively high speed. You have to find the sweet spot for you given your 1) bow, 2) draw length, 3) draw weight. Ideally you want to maximize kinetic energy. The shorter your shot distance and smaller/thinner your target animal the lighter you can go on arrows. If you shoot long distances or elk (or even Kansas whitetails) you're going to want some extra mass in your arrows. Get a quality target (Block or Mackenzie, etc.) if you're going to shoot a lot. If you're not sure yet then you can pick up a cheap-o Cabelas layered target but they won't last that long.
Next: shoot, Shoot, SHOOT. A lot. But build up to it. Don't try to shoot 100 arrows your first day. Maybe just shoot 6. More if you can, but when you get tired and you feel form starting to break down then stop. I like to shoot a dozen arrows every morning. Then sometimes I shoot 40-60 in the evening. Keep in mind 2 things: 1) I haven't flung an arrow in 2 months thanks to work so I'm not exactly practicing what I preach currently; & 2) When I am in a shooting routine I shoot A LOT MORE than most people. In fact if you even shoot 100 arrows a week you'll be shooting way more than most. Start with your poundage low enough that it is very easy to draw. Don't start heavy and develop bad habits. You need to be able to hold your bow at shooting height and then draw without the bow ever rising or dipping. If you can do that at 70 pounds great. If it's at 50# that's fine too. Gradually work your way up in weight. You've got all summer to get to where you want to be, you don't have to start at full poundage. Yes, each time you increase your draw weight you'll have to re-sight your bow in, but frankly it's good practice. Once you get close to hunting season (say a month out) then stop changing your draw weight, dial your pins in and stop fiddling with them. As you shoot, film yourself from the front/side/back to see what you're doing right, and what you're doing wrong. Gradually move your distance back as you get better (3 pin sights can easily get you 20/30/40yards). Don't be afraid to step back up nice and close if you have a rough day.
That should really get you started, but doesn't even begin to talk about the other aspects of bow hunting deer in terms of shot selection, deer body language. Stand selection, stand prep, wind, scent control, etc., etc., etc. I still don't have that all figured out either so if anyone has helpful tips I'll gladly listen.
TLDnR: Get a pro-shop to measure your accurate draw length. Get the best bow you can afford. Don't scrimp on your rest or release. Pay your pro-shop to help you set-up and tune your bow. Then shoot as much, and as often as you can.
