Make sure your hoses are attached before turning on your air, check that you can inflate your bcd and breath okay out of both your primary reg and your octo.
Unless you’re going straight into the water after setting up your gear, turn the air off after setting up your gear and making sure you have enough air in your tank for the dive (if you have a long boat trip and somebody’s gear lands on top of your reg, you could lose all your air by the time you get to the dive site)
Make sure you turn your air back on