I'm not a Dom by far but I do know a little about it:
This link has descriptions and pictures to ensure you do it the right way:
http://ladyjulianna.blogspot.com.au/...1080fd89f92d35
This may help as a start.
A few safety things to remember:
Use rope and not string and avoid knots.
Always have a pair of scissors (or side cutters) handy. (Imagine a badly swollen pair of cock and balls and trying to find a thinish string to cut it loose...)
The cock and balls can safely endure quite a lot but some care must be taken while it is tied up tightly as 'bursting' happens and will cause irreparable damage.
Enjoy! xxx