I can’t remember ever going on a dive a trip and not seeing at least one diver ending up with their tank coming loose during the dive. Most often this is due to not tightening the BCD tank strap or not weaving it properly through the buckle. There are many professional divers (instructors & divemasters) who don't know how to do it either so don't feel bad. Learn to do it correctly and you'll be someone's hero one day when you show them and save their dive!
Watch this video that Norbert and I put together to learn how to weave and tighten the BCD tank strap.