Type of string: To start with, it can be better to use slightly thicker string than you might normally use, as it is possible to burn yourself on the string. Once you get used to it, you'll start to know what works for you best.
String length: I use quite a large loop, so I can use it in different ways, as I'll explain on the next few pages. The string is a little shorter than twice the length of my normal diabolo string.
Knot: You will need a secure but small knot. I use a double figure of eight knot, pulled very tight.
Gloves: As I said, it can be easy to burn yourself on the string. I'm told that white gloves (the 'magician' type) are good if you do start having problems. I don't wear gloves, so deliberately do tricks that are less likely to burn my fingers!