Learning how to prune a magnolia tree can help you to keep it in good shape so that it flowers well for many years to come.
The good news is that magnolias don't tend to need much pruning. In fact I am sure that many magnolia trees grow perfectly well and develop into fine specimens with no pruning at all. But if growth becomes unbalanced, or if branches are damaged in a storm, or if branches start rubbing against each other wearing away the bark so that rots set in, or if new growth ruins the shape – then something needs to be done.
Also, when you pick out your own new magnolia at the nursery you will be sure to take home a well-shaped plant. Mail order arrivals, however, may need a little pruning to improve their balance at a young age.
Before learning how to plant a magnolia tree, it's always a good idea to stand back and take a look at your new magnolia, to assess whether or not it needs pruning before putting it in the ground.
Mature magnolia trees typically develop a naturally even and elegant shape without any pruning at all. They usually only need pruning if they are damaged in a storm or if they are outgrowing their space.
Remember that tall trees and even mature shrubs can be difficult to work on – especially if you need to use a chainsaw. So unless you are experienced at this sort of work, or can do the job comfortably from a regular folding step ladder, hire a qualified arborist to do the work for you, rather than attempting to learn how to prune a magnolia tree yourself.

If a dramatic rejuvenation is necessary, cutting back very hard to significantly reduce the size of the plant, do so in spring as growth is beginning.

Your magnolia may have been neglected, but that does not necessarily mean that it needs drastic treatment. It may be that maintenance pruning – removal of dead growth, branches rubbing together and branches that disrupt the elegant shape is all that’s needed.
However, if more drastic treatment really is necessary, magnolias will shoot from quite thick branches and even from a stump.
One thing worth knowing about how to prune a magnolia tree is that both evergreen and deciduous types can be cut back hard – or even to a stump – as the buds are bursting in spring. However, think carefully about applying this treatment to single stemmed magnolia trees as it will prove very hard to replicate their natural shape. This approach works much better with bushy magnolias.
Also, pruning large shrubs, and especially large trees, is a task for a skilled arborist who will have the training and the equipment to do a good job – not to mention insurance in case something goes wrong. It is a mistake to be overambitious, whether that's with pink magnolias, or any other type or color of magnolia tree.

Some magnolias are very difficult for nurseries to propagate by rooting cuttings so they are propagated by grafting the named variety on to a seedling of a different species, the rootstock. But the rootstock can sometimes throw up shoots that are not only entirely different from the variety you want to grow, but are so vigorous that they start to take over.
Remove them by scraping away soil to reveal where they emerge from the root, and cutting them off close.