Those "trap door" split back frames make it easy to keep the paper and neg in place. Line up the neg and paper and put it on the glass and hold it with one hand while you take half of the split back and put it on the paper opposite your hand. Keep pressure on the split back and put the springs in place - it works like a charm.
That's the process I follow, simple and repeatable. Works great. Definitely worth buying a nice frame.