Deciduous magnolias such as Magnolia x soulangeana are prone to bleeding sap if pruned early in the year so it’s best to wait until after your magnolia has flowered and prune it in early to mid-summer. When you prune, make an angled cut slightly away from the main branch or trunk leaving a small amount of the branch intact. This protects the ‘collar’ which is where the branch meets the trunk. You should end up with a stub about 2-3 centimetres long. You will need to make an under-cut or support the branch when sawing it, to prevent the branch tearing away from the trunk before you have completed the cut. There is no need to apply any tree wound paint afterwards as this tends to seal in any pathogens and moisture rather than allowing the wound to heal naturally.