Cabbage is a greedy plant and needs rich and firm soil, preferably in a spot where beans grew before.  Apply manure before planting. If you are planting in a pot, don’t buy multipurpose compost as it has a very loose composition and nowhere near firm enough. Before planting, check if it’s a summer or winter grower.
 
Suitable companion plants are: dill, camomile (their pungent scent wards off pests) and nasturtiums (caterpillars prefer eat more delicate leaves of nasturtium rather more tough cabbage leaves).  Alternatively, you can cover your crop with a fine mesh.
Cabbages belong to the leafy vegetables group of plants and therefore need to be fed and watered regularly.