If your BBQ grill has been sitting idle for months, it's a good idea to take a close look at its components to make sure everything is in proper working order. Examine hoses for any cracks or damage. If a hose seems compromised in any way, replace it.
Inspect burners and their gas tubes and make sure they aren't worn out, rusty or blocked by debris or spider webs. If gas tubes have worn spots, replace them. If they are blocked, use a pipe cleaner, toothpick or paper clip to clear them. Check knobs and other controls to make sure they're undamaged and working properly. Tighten any loose screws or bolts. If your propane tank is empty, refill it at an authorized propane supplier.
To avoid serious injury, be sure the propane tank is disconnected from the grill before doing maintenance. Read your BBQ grill's instruction manual for particular safety issues.