While diving last week I realized how poorly most divers check their regulator. Thoroughly testing your regulator takes less than a minute, and greatly eases my mind before a dive.
First, I see a lot of divers check their primary by pushing the free flow button. This is insufficient for me. I prefer to take a breath or two off of the regulator, which ensures air is pulling properly through the hoses and diaphram, not to mention avoids wasting precious air; air comes out fast during free flow!
The second oversight is one I am particularly guilty of. Many divers never check that their secondary is functioning properly. Simply repeating the same test of taking a breath or two greatly reduces the chance of a problem underwater, should you or your buddy need backup air.
Try this next time you dive. If the primary or octopus appears to have even a slight problem, I wouldn't hesitate to ask the dive operator for a replacement. No shop worth your money would have a problem assuring the safety and peace of mind of their divers--their reputation depends on it.
Every extra precaution makes for a safer dive, so begin establishing good habits and test all your gear properly.