Light prune after flowering. Cut out any straggly bits, take off dead flowers and light prune to a nice shape.
They don't usually need pruning, mine is in a large pot and it looks after itself most of the time.

Ours will get a drastic pruning after flowering, they are in the ground and have got far too big for their boots - probably because we have not pruned in previous years... I checked with a couple of nursery men and you can hack this back seriously hard, i.e. less than a foot in height, and it will still grow back. One of our two will get a light haircut the other is going to be taken back to the one foot level...

That's good to know for me too, thanks. Mum has 2 in the ground and she was asking.

Seabird we have been told to cut back as hard as we need to! I do confess to a slight concern... However, given the folk we asked advice from I guess we just have to go ahead and do. In our case with a pieris it is either prune back seriously hard or remove... so prune back hard is first step :-)

Well, it has a 50/50 chance as we say. Good luck. Maybe a light prune every year for the average pieris is the answer. Maybe that would prevent them getting out of hand.

I had an 8ft Pieris damaged by a falling branch 3 years ago, had to prune it to about 2ft. It came back as beautiful as ever. It's over 5ft tall now