1. Money. I'd say $800 for a decent entry level setup. $1000-1200+ if you can swing it.
2. Bow. Get measured and try different bows to see how they feel. Used bows can be sketchy because you don't know what people have done to them, or if they'll fit you well. New bows are best but used bows have terrible resale so you can get a good deal on one.
3. Release. Get a good one.
4. Accessories. Rests, stabilizers, sights, etc. You can go crazy with this. Work within your budget and ask questions on here and to shop guys.
5. Arrows and heads. Again, ask the shop guys about weights and brands. I'm happy with the Victory stuff I've been buying from Bow N Arrow but maybe other folks think different.
6. Target. Either go to a range and/or buy one for backyard shooting if you can swing it. I used to shoot a lot at Morley Field for $2 a session. Cool peeps.
7. Time and practice. Have experienced people watch your form. Just like a golf swing or baseball swing. Really helps.
Larry would be proud of the length of this BTW