From: Naples Island- Long Beach CA - Southern California
What you are looking into is a bit of CBT. While CBT stands for cock and ball torture, not all of it is painful. Few tips.. when you tie, do not use shoe laces.. those bad boys are meant to take a knot and hold it. Also avoid rubber bands. It can be hard to get them back off.. (you do know they castrate cattle with little rubber bands, right?)
Blood supply is a big thing in any type of bondage. You do not want to isolate any part of the body from blood flow for very long. I'm not going to give you a "safe" length of time.. look it up yourself. There is a book called The Family Jewels that goes over safe CBT. I own it and it is a good basic resource.
To start with, do not tie things overly tight. Try wrapping and tucking the ends under another strand rather than making a knot. I do a lot of CBT and I never make a knot when "tying." If you want the feeling of constriction in a bit safer incarnation, try gates of hell. This is put on a man when he is limp and it cuts into him a bit when he gets hard. There are versions that have snaps so they can be removed while he is hard; a regular gates of hell can not. Another way to get constriction is an ace bandage. You wrap the entire cock and balls up like it has a sprain. I don't know I'd feel comfortable doing it to a limp cock and then encouraging erection. I've only done it to an erect penis.
I highly recommend you go slow in this area. Make sure to do your research before doing it to yourself or letting someone else do it to you. While you should always trust the person you're playing with, you are also responsible for knowing the ins and outs of safe play yourself. You're the one who has to live in that body for the rest of your life.
There are a lot of photo examples of CBT in my Ygroups. You can get to them from the link in my sig,
*Do not threaten the weak. Intimidate the strong. ~ Stevenson*