I have an Oleander in a pot which flowers but I would like to know how to prune my plant.
If you are going to keep it indoors, you can prune any time between the end of flowering and spring.
If you are going to keep it in a cool place, wait until mid-spring.
Did you your oleander grow well? If so, it means it can take a bit of pruning to really hard coppicing,
and it will come back nicely once the weather warms. I fertilize my potted oleander heavily every year,
and I think you should do this in spring as well.
I have a large oleander in a large pot outside and will be pruning around the end of March (you don't want frost damage on the young growth that will result) I also fleece it in winter to be on the safe side. It is no problem in England where I grow it quite dry, but it needs water in hot spells over here in south of France because the ones here are also in pots.