To the original poster:
I will chime in my answer, although there were a lot of good points brought up already about how to get better penetration.
I would say the most important thing is an accurate shot. You should practice every day with 10 arrows, even during the season. This will give you confidence that your bow didn't get knocked out of whack somehow, and also make everything automatic when bucky is out there. Things tend to happen very fast, and lots of decisions are made in a short time. You want the process of sending an arrow out after the deer to be completely automatic. Those shoulder blades stop a lot of arrows from passing through, and a shoulder blade is always a bad shot.
What is tied in with an an accurate shot also is a well tuned bow. Hopefully you aren't like me several years ago when I needed my bow tuned and all the local pro shops wanted to do was adjust my grip! I learned all of this on my own, after hours and hours of reading, and then experimenting with my own bow. Easton has some wonderful articles talking about how to tune a bow, and they also have charts on a properly sized arrow. The arrow must be spined correctly - when fired from the bow it must give a little, but not too much. You are exactly like me years ago - WTF does spine mean? Also you must paper tune your bow, this will tell you exactly what the arrow is doing. When your arrows go in the target, are they slanted in a certain direction? This means they are not flying true, and will not have the penetration that is so important when it comes to killing a deer. Also, a bow can be tuned wrong but still not show it when shooting field tips - but paper tuning will reveal it. If you are shooting fixed blades, you must have some practice arrows with blades to ensure that they fly correctly at the target. Many times a bow slightly out of tune with field tips becomes a lot out of tune with broadheads.
And lastly, and I must admit I am surprised in a good way about this (by all the people on this forum who understand), you need to learn about momentum vs kinetic energy. Kinetic energy is very important because it talks about a bows energy, and also gives the bow manufacturers a reason to persuade you why this years model is better than last years. But when it comes to killing a deer, momemtum means everything. Put your house on some railroad tracks, and then send a freight train at full speed headed toward your house. It will crash through your house and then keep on going - that is basically what momentum means. Does that make sense? It is very very important when killing a deer because you want the arrow to crash through a tough hairy hide, sinew, tendons, and bone on it's way through. You want to shoot the heaviest arrow you can that will fly true - this may mean using 125 grain broadheads, heavy arrows, etc. This comes at a cost - you will no longer have the flat single pin shooting bow good out to 45 yards. Do any of your buddies shoot 75 grain broadheads? They are great for target shooting, but not for killing a deer. I used to use a lighter broadhead, until I learned what all of this stuff means. (after I lost a deer and was sick about it) I have to hold high at 30 yards when I shoot, but I always try and sit where the maximum shot I can actually take is 25 yards or less. A heavier arrow will hit harder every single time, kind of like some snottly little kid using a sling shot on you - with a plastic pellet vs a ball bearing.
It would be nice if every arrow went between ribs when going through both lungs, but your odds are high that you need to break a rib to go pass through. Ever hear that sound like a stick breaking when you shoot a deer? That is a rib snapping.
You will learn as you research this stuff that it all is a balance - a heavier arrow penetrates more, but requires the shooter to know his distances better when shooting. A mechanical broadhead may do more damage and be more forgiving on the entry hole, but requires a bow with more energy (higher draw strength) to do that damage. Given the same bow, I believe a fixed blade will penetrate more than a mechanical because some energy is lost when opening up- this is why higher poundage is required for mechanical broadheads. Holding a higher pound bow also means flatter shooting arrows, but at the same time, how long can you hold a higher pound bow still while bucky is making a scrape with his vitals behind a tree? Do you see what I mean by it all being a balance? And everyone has an opinion that is different - buy this broadhead, use that bow etc. My advice is to learn as much as you can, and then experiment with your bow.
And lastly, but certainly not least, whatever broadhead you use, it must be razor sharp. Don't even think about shooting a broadhead through a practice bale and then taking it out hunting. Those arteries in a deer are tough and thick, and you want the sharpest possible broadhead slicing through the artery, not just running along it.