Use wood pellets made for pellet grills; Traeger recommends its own. "Never use heating fuel pellets" (the manual).
Store the bags sealed, dry and away from heat.
Check them: good pellets "have a sheen and a nice snap". Dull, crumbly pellets and sawdust cause temperature swings and failed starts (Traeger support).
Keep the hopper lid shut and the grill covered: wet pellets swell and jam the auger (the manual).
Never add pellets by hand to a hot firepot (the manual).
Empty the hopper to change flavour
The manual, page 23. The clean-out door is on the back of the hopper.
Switch off, unplug, and let the grill cool completely.
Stand a clean bucket under the clean-out door: "a clean 19-litre (5-gallon) bucket works great".
Unscrew the clean-out door fastener and open the door.