Wubber and Beadsmith (and many others) make great mandrel pliers. One thing I like to do is measure and label each side of the pliers, so I can easily grab the size I need.

We all know that the need for different shapes and sizes of jump rings is a necessity. Things to consider when deciding on your jump ring usage.... What is hanging off the jump ring, where is it in used on the jewelry, how heavy the jewelry piece is.
I like to use round jump rings in heavy gauge wire, such as 14g - 18g. With the thicker wire, there is a little chance of the jump ring opening and you losing your bracelet or necklace. You can certainly use smaller gauge wire but it is not as sturdy. Another trick that I will use is to double up on jump rings, adding an additional design element but also adding strength to the links. Beadsmith has a great round mandrel kit.

I use oval jump rings when I making earrings or near a clasp. With the opening on the side, there is less of chance for the components on either side slipping off. Beadsmith makes an oval mandrel set that is awesome.

You can use many things as a mandrel, an ink pen, a dowel, a pencil. There are also bezel mandrels in different shapes but I will talk about those in a later tip.