From Scuba Diving.com
Your equipment. Obviously, you need to be properly equipped and your gear has to be in good condition. Not so obviously, none of your equipment should be brand-new on that deep dive. In order to stay calm and able to handle the unexpected, you need to keep your “task loading” to a minimum. At depth on a 110-foot dive is no place to forget which is the inflate button on your new BC. Or to discover that your new mask fogs. You should feel confident with your gear before you go deep.
Your buddy’s experience and equipment. The least-prepared buddy should determine the limits of the dive. Resist the temptation to exceed your buddy’s comfort level (“Relax. You’ll be fine!”) or your own (“I guess he knows what we’re doing”). When you’re nervous about a dive, pride and the fear of admitting fear can make it hard to face the truth.
The conditions of the dive. In many ways, “deep” is relative. A 110-foot dive in warm, clear, calm Caribbean water is probably not as challenging as a 70-foot dive on a cold, current-swept New Jersey wreck. What counts is the total stress level. Depth is one stress–others are cold, current, low visibility, surge, equipment load, anxiety, fatigue and more.
Surface support. Is someone staying with the boat to make sure it stays anchored, and to render help if it’s needed? Is there oxygen on board? A radio? Will an ascent/descent line be deployed? A hang bar? Is a recompression chamber reachable within a few hours? Do the divemaster, the boat captain and the diving operation inspire confidence?
Your motivation. Finally, ask yourself why you are considering this dive at all. Because you want to see the wreck is a valid reason. Because you want to make a moderate and prudent expansion of your deep diving experience to help prepare you for that dream trip to Truk is valid too. “Because everybody else is doing it and I don’t want to look like a wimp” is not.