Do send your child in clothes they can pull up & down themselves. There's nothing worse than a potty training child coming into nursery in dungarees. Yes they look cute, but when it comes to potty training they are the devil's plaything! 90% of children I've seen who've come to Nursery in dungarees cannot undo them by themselves.
Don't put your child in a pull-up for months & expect potty training to just happen. I'm not a fan of pull-ups, they're basically nappies shaped like pants. A child needs to feel the wetness from having done a wee and pull-ups just don't achieve that. Plus some children can be lazy and would rather do it in their pull-up than walk to the bathroom and use the toilet.
Do send your child into Nursery with lots of spare clothes- underwear, socks and bottoms are your best bet. (I've seen far too many children with 10 tops in their bags but 1 pair of pants & 1 pair of trousers!) You can pick up packs of underwear, socks and leggings/tracksuit bottoms cheaply in Primark/supermarkets.
Don't yell at or belittle your child if they do have an accident. Accidents happen to all, even those who may have been toilet trained for a while. Telling your child off makes them feel ashamed of what they've done, and they're less likely to want to admit when they've had an accident in the future.
Do be prepared for having extra washing. Again, accidents do happen. One parent I know off will automatically throw clothes in the bin if her child has done a number 2 in them rather than wash them!
Don't send your child to Nursery in their favourite pants/trousers/skirt/dress. I've had to look after several completely distraught children when they've had accidents and wet their favourite clothes