Are you storing the drums inside or outside?
If outside rest the drums on their side, on supports or blocks that keep the drums clear of the ground & moisture, and with the bungholes level with each other.
Well prior to use move the drum to the fueling point. Position the drum upright but with one side on a block so that the drum is slightly tilted. The high side needs to be the same side as as the bunghole the pump will feed from if you'll cover the top of the drum or, alternatively,position the block between the bungholes so that neither of them is on the low side. The idea is that any sediment or water will settle at the low point, away from the bottom of the pump's standpipe and also the bungholes are protected from water too. One US gov. document recommends 1 hour settling time for each foot the drum had to be moved. I usually positioned drums the day before if possible, or 1st thing in the morning for a planned afternoon refueling.
Get water finding paste or paper and test the drum fuel prior to use.
Use a pump with a filter attached. Even better, obtain a monitor which will warn if water is present.
Make sure everything is earthed together before opening any caps or bungs.
Replaced the bungs in the drum after use - especially if there's still fuel in the drum you'd like to use later. Also keep the pump protected from moisture.