Bow
Buy the best bow you can afford. If you don't you will just buy a new one a few years down the road because the one you have either does not have enough power or accuracy to fit your needs.  Go with a bow that has less radical cams and that is longer in length. I believe this makes the bow much easier to tune when bow season arrives.

String and sight
Use a peep sight or a kisser button to get the most out of your sight. Without one no two shots will be consistent. If you get a new string put on your bow, take at least 100 shots, then have the draw weight adjusted to what you wish to shoot with before adjusting your sights.  This gives the string a chance to stretch before making adjustments.  If you bow gets wet while in the field, let the string dry and then make sure to pull it back several times to full draw before shooting at a potential target. I have found that strings that get wet and they dry can shrink a little making you first couple of shots go high. I always pull my bow back once when I get set up in the field just to make sure everything is ok, the arrow is nocked properly, there are no noises etc.  I highly recommend the new "Zebra" brand strings that are now available.  They have strands twisted in opposite directions so that when you pull back the string doesn't tend to twist as much and your peep sight stays put.

Broadheads
Two bladed broadheads fly closest to field points because they wind plane much less.   They also provide maximum penatration for greater chances of recovery of the animal (see ethics). Three blade and four blade broadheads tend to be affected. Mechanically expanding broadheads will fly true but may introduce new failure modes into the picture.

Draw weight
Don't go with a higher draw weight than you can handle. A well placed arrow shot with a 50# draw weight can easily take a deer. Remember that the draw weight that doesn't feel like too much now, can be a lot harder to handle when it is 20 degrees outside and you are wearing heavy clothes. Practice shooting you bow from a treestand at a height representative of that you will hunt from. Practice shooting while wearing the same heavy gloves, hats, face masks, etc, that you will be wearing in the field.

Arrow and broadhead weight
Make sure that you practice with the same field tip weight as the broadheads that you intend to use.  Your total arrow and broadhead weight must be a large enough to prevent a situation similar to a "dry fire" of your bow.  Consult the current Easton (or other) charts after selecting your broadhead and draw weight to determine what arrow you should use.  The arrows are selected for both their weight and spline (ability to bend when fired).  Ideally arrows with the broadheads on, should be approximately 10% front heavy.  This means they would balance at a point 10% towards the front of the arrow from center.  Make sure when a broadhead is mounted on the arrow shaft that you spin the arrow on the tip of the broadhead.  There should be no noticeable wobble.  If there is, try another broadhead or try the broadhead on another arrow.

Noise
Try to eliminate all noise with your bow. This means lubricant on all moving parts. Draw an arrow back, listen for any noise.  Use a Teflon spacer on your cable guide, not a cheap plastic one.  A arrow rest with rubber coated wheels may be the only way to get rid of all noise that occurs during the draw of the arrow.  It is unbelievable how loud your bow can sound on a silent morning.  The new limb saver devices that are out now are the best thing since sliced bread.  You will not believe how much they quiet your bow down.

There are 1000 things that can go wrong when that big buck wanders under your stand.   Try to eliminate as many of them as you can. I have only eliminated three or four hundred of the thousands of things that can defeat you.