There may be a thread about this alread and if so could someone please direct me to it?

I'm going to try using a breast pump in the next few days to try and bring on labour, but I'm not sure what to do exactly. I've got an electric one and I had a small "play" with it today. I don't know how much suction to use and I was scared of it hurting so I hardly used any suction at all, didn't really feel anything. Should I feel pressure? How much is too much?