Succulent plants are very forgiving and are waterwise. They thrive on neglect! When planting up a pot one needs to have these three elements, a "Thriller", some 'Fillers" and some "Spillers." I would choose a Kalanchoe sexangularis as the "thriller" as it has height and turns a beautiful burgundy in winter. The "fillers" would be Crassula capitella and Cotyledon orbiculata with it's lovely grey leaves. The "spillers" would be Portulacarya afra prostrata and Aptemia cordata as they will both spill over the edge of the pot. It's always a good idea to group pots with similar plants.