I have a bright light over head and slightly off center on the bullet seating side so I can check the powder charge before putting the bullet on the case. When setting up, I weight ever charge for the first 20 cases or until the weights settle where I want them.
I take a case out of the dillion just before I pull the handle to charge the case, put it on the digital scale zero it, then put it back on the press pull the handle then weight the case, charge and all. (be careful not to deprime a newly primed case on first die)
If you are not using all four positions get a low powder sensor from dillon for the open station.
If I am loading Match ammo I weight about every 10th charge. For shooting ammo I check about every 25th to 50th charge.
I also wipe the lube off all my cases with a rag after reloading and shake the case (when not using a compressed charge) to hear if the case has powder in it. You can tell if their isn't enough.
Also if you have a digital scale put a round on it, zero, and then place each cartridge in it in turn if you find a loaded cartridge the is say 5 or 10 grains lighter or heaver than the others it might be a canidate to pull apart to see what is there.
as far as accuracy goes, my dillion 550b is ususlly with in .2 grains with an extruded powder with a hopper that is at least half full and the powder has settled.
Try this get a pound of extruded powder,pour it in to the hopper just before bed and then put the cover on it and use a piece of tape to mark the level. Then come back the next evening and see if it hasn't settled. I have seen a pound of IMR 4350 settle as much as a half inch, and thats just setting overnight.