Greengage pruning

Hi, does anyone know how to prune a container grown Greengage? This is the second year it has been in a large container and produced some very, very sweet fruit this year although some of them fell off and looked a little diseased. I did water it regularly and fertilised with Miracle-Gro. I didn't prune it last year so will probably do it this year if I know what I am doing.

Thanks

Brian