How Should I Prune A Flowering Plum Tree?

A flowering plum tree (prunus blireana) would benefit from pruning, as it would remove dead and diseased wood, as well as encouraging new growth. However, it can be difficult to undertake. It is better to prune when the shape of the plant is visible, rather than when the branch is obscured by leaves. The best time to prune a plum tree would be during their dormant period, which is usually early spring. Some of the techniques you can use to reduce damage to the tree include thinning the crown, which involves removing a few weak branches. You can also raise the crown by pruning lower branches, or reduce it by cutting away some of the larger branches at the top of the tree which inhibit growth. The best way of pruning a branch is to cut it about ¼ inch from the bud, with the bud facing outwards. Also, with larger branches, cut about a third through the branch to prevent damage to the bark. Pruning shears, lopping shears, hedge shears and hand saws are the most common tools, although it is recommended to seek professional help to ensure a lack of damage to the tree.

I heard you should trim back all horizontal branches and leave the vertical limbs so sunlight could penetrate the tree. Is this correct.  Oklahoma

Even with the ground.