Overwintering plants is a good way of keeping tender, and less hardy plants, from year to year. Which plants you can overwinter depends really on your available frost free space.
If overwintering plants under glass, the main problem is likely to be botrytis, grey mould particularly in a green house. Winter plants need good air circulation to prevent mould. During cold spells it is tempting to wrap up the plants and block off all the draughts, but this will create just the still damp conditions mould enjoys.
To reduce the risk of mould, space plants well apart, avoid their leaves touching and prune if necessary. Water sparingly, open vents and doors as much as possible and raise plants off the ground on a trestle, see image. At the first signs of mould, which forms on leaves as grey fuzzy powder which collapse to the touch remove the plant and any leaves to stop it spreading.