It would be helpful to know if you own an evergreen magnolia tree or a deciduous magnolia tree or shrub (one that loses its leaves in fall).Also, whether you live in a climate where the flower buds may be getting killed. (Sometimes "microclimates" in a yard can mean your plant is harmed by frost (or protected from it) when the opposite is true for your neighbors.
You don't say whether your tree has ever bloomed. A common Southern magnolia (
This is often true if you buy a small tree that's just marked "magnolia" (or dig a young tree from your woods). Or if it was grown from seed. It's always better to buy a magnolia that has a cultivar name ('Edith Brogue' or 'Little Gem,' for instance). Named magnolias are bred to bloom when young.
Both evergreen and deciduous magnolias prefer sun and will bloom less when they're in shade.
Are you fertilizing? If not, spread an acid granular fertilizer (such as the kind sold for azaleas, camellias, and rhododendrons) in a large circle around the base of the tree once in early spring and water in well.
If you're fertilizing frequently, the plant may be putting on new growth at the expense of blooms, so it would be good to stop and see if that helps.
Watch out for drainage, too. Magnolias don't like to stand in water.