Don't rely on someone else to watch the time, your depth, etc. If you don't feel right about going somewhere or doing something, say so. In order to keep your equipment from dragging, use Velcro strips to keep your gauges close to your BC jacket. Always wear some kind of wetsuit or dive skin, no matter how warm the water is. Bring your own wetsuit.
Rentals are kind of nasty.
Bring a flash light It can be difficult, but finding a regular dive partner can really enhance your diving. Safety Number one rule for safety is stay calm. Panicking underwater just magnifies any situation making things worse. If it's been over 12 months since your last dive a refresher course is suggested. Planning your dive is vital to having a safe dive.