Most plums root quite easily so chances are good.
Cutting mix should be inert, well drained but still hold moisture. I use 50/50 coir peat/ perlite. Sand/peat is also ok or just buy a small bag of propagating mix at the garden centre.
Rooting hormone does help so get some and dip the base of the cutting.
Humidity is important so the cutting does not dehydrate while it has no roots. Cover the pot with a plastic bag or keep the pot in a larger plastic tub with a lid. Automatic misting is used by commercial propagators.
Keep your cuttings damp but not too wet. Place in a well lit area but not full sun or you'll cook them.

and wait until you can see new roots coming out the bottom of the pot before potting them up in proper potting mix.
Good luck