Here is a little information on how to properly crimp ring terminals.
Step 1. First you need to figure out the correct ring terminal to use per the application.
A great post to look at for help with picking the correct terminal is here.
In this post I am going to use part number WM18273-ND (which is 18-22awg), from Molex.
Step 2. You will have to find the correct Crimp tool for the terminal that you will be using. These can be found on the Digi-key website, Manufacturer website or manufacturer datasheet.
With this ring terminal I will be using the Crimp Tool WM9986-ND from Molex,
Step 3. Make sure you strip the correct amount of insulation from the wire. Here is a Application Tooling Specification Sheet from Molex that will have the terminal part numbers on it and will state the correct insulation strip length.
In other cases the wire strip length will be the length of the crimp area.
Another option on an insulated Terminal is to measure the insulation part from the lip to the end of the insulation
Also check out forum post
Step 4. Crimp the terminal. Take the crimp tool and place the terminal into the jaws of the crimp tool. Match up the color of the terminal to the colored dot on the die set of the crimp tool. This will match the correct awg size.
Align the terminal so both sides of the insulation are flush with the edges of the die set and close the jaws enough to hold the terminal.
Insert the wire and crimp the terminal onto the wire by squeezing the handles until they release.
Step 5. Inspect the crimp. Make sure the crimp is done properly.
Here is a document called Industrial Crimp Quality Handbook that will have all the proper information on a correct crimp and testing it.
This procedure can also be used for other terminals such as Quick disconnects, Spade, Wire Pin, Knife, Barrel/bullet and Rectangular Terminal Connectors.