I’ve tried it a few different ways and the best outcome I’ve had was using some tubing, like this one: youtu.be/yuZ0DA8w9XI

I don’t always do it but when I do, I do it this way from now on. The tube makes sure the filament stays aligned, I also cut the two ends at a 45 and try and join them up inside the tube. Usually I’ll save the ends and then do a few rolls at once, can usually get another few prints out of it.