So that the end of the beading wire does not scratch the wearer, make sure your last bead or two on the necklace is large enough so that a small amount of extra beading wire can be threaded back through. I have found that 4mm sized beads work very well for this.
To keep the loop of your beading wire large enough, try inserting one side your your round-nosed pliers into the loop while you pull the wire tight.
Use sterling tube shaped crimp beads rather than the base metal round beads. They are much easier to work with, especially for beginners.
Do not expect perfection on your first, second, or even third try. As with any other jewelry technique, this takes practice in order to perfect your technique.
Get a nice pair of crimping pliers, and do not try to fake a crimp with a regular pair of pliers. It just is not the same. Most jewelry and beading suppliers carry crimp pliers and crimp beads.
Make sure you use the right crimp beads with the right sized pliers.
