Really echo the point about waiting until they're ready - almost until they're too old, if you know what I mean. What's the point of rushing it - it's not as though someone is going to report you to social services if they're not potty trained by 'x' months.
We also waited until we had a clear few weeks to devote to it - not too many appointments or need to rush around. I made a big thing of talking up the idea of using the potty / toilet with DD (who was 2.5 when we started trying). Then we went out and bought some really pretty 'big girls pants' (pink, with bows on!).
To start with though, I left her pants off, and just put her in shorts / trousers. The pants were actually quite confusing, as she thought they were just prettier versions of pull up nappies. She couldn't understand why they got wet. However, maybe this was what helped get the message across.
I kept one potty upstairs and one downstairs, and reminded her every so often. I have also always let her see me going to the loo - right from day one - as I think it's very hard to expect them to know what to do if they've never seen it before!
We had loads of accidents to start off with, then, within a few days, she'd got it. We still have the odd accident if she's tired, or preoccupied with playing with something. But nothing awful
We also (selfishly) delayed things until we'd got new hard floors downstairs, rather than the carpet! Makes cleaning up accidents much easier.