OK - This is the very limited amount I know about it - so I might get it completely wrong!
I think the whole idea of it is to stimulate the hormones like a baby would during the first stages, so it you are going to do anything, it probably needs to feel like a baby action.
I did it whenever I got contractions/BH's (I had 2 weeks of prelabour so there were plenty on a pretty regular basis!). I would hold a warm facewasher/wheat bag to my chest and then start basically milking each one. I also used a breast pump and got alot of colostrum out.
As for what they did - well pretty much nothing for me. They did sort of feel like my contractions were a little stronger, but since Jenna was in the wrong possy, nothing natural was going to bring on labour for me until she got into the right position.
I also got DP to have a good suck on them, and that did about the same as what the breast pump did.
It was quite exciting at the time, cause like I say the contractions would deepen, but then just go away again.

Tanya (who isnt around that much at the moment) used nipple stimulation in her last birth and it seemed to work for her.

HTH - maybe someone will pop in and give you a more detailed description of what to do