lots of bribery ('special treat = three chocolate buttons for each time dd used the potty) also - sticker chart.
lots of patience
don't get cross (difficult when knackered)
potty in front of tv to start with!
if it's clearly not working, don't push it.
wait until he/she is really really ready then it doesn't take much time.
take advantage of the good weather and do it outside.
get everyone on board with you (dh, childcare, any other carers like grandparents).
lots of praise (we rang daddy at work and left a long message about first poo in potty which he said was the funniest, best one he'd ever had).
keep asking whether they want to go, and if it's been a while, even if they say no, insist they have a 'go'.
get them interested in what happens in the toilet first. dd still loves the fact that 'daddy's having a poo'.
nappies on for sleeps
that's a start anyway.
good luck (it's fab not having to buy so many nappies!)