Credit: Nightshade Eld
The art of flight is a complex one that relies on the ability of the user to understand air currents, how to angle the body, and the aerodynamic forces that allow one to sustain flight. Two fundamental ideas that need to be understood to begin learning to fly are lift and drag. Lift force is produced by the action of air flow on the wing, which is an airfoil. The airfoil is shaped such that the air provides a net upward force on the wing, while the movement of air is directed downward. Aerodynamic drag is the force opposite to the direction of motion, and hence the source of energy loss in flight. The drag force can be separated into two portions, lift-induced drag, which is inherent in the wing (primarily arising from wingtip vortices), and parasitic drag, including skin friction drag from the friction of air and body surfaces and form drag from the bird's frontal area. The streamlining of bird's body and wings reduces these forces. A force that must be provided by anyone who wants to fly is thrust, thrust is what moves something forward.
When in flight one must produce enough lift to counteract the effects of weight, by flapping a pair of wings for example lift is created that moves to create thrust which in turn creates even more lift that can help maintain or increase height in the air. Certain things can be done to make this process easier such as curling in wing tips to conserve energy. Constant adjustment needs to be done in order to get the proper angle while in the air. Gliding through the air is another form of flight which requires no energy use, however one will be at a constant decline in height unless they know how to properly ride air currents.
Many aspects of flight are determined by size, body shape, and wing shape. Smaller creatures can simply jump into the air for take off and easily catch a wind current. However larger creatures must face into the wind and catch a draft before they can properly take off. Ideally they will be able to perch on a cliff or branch where they can better jump into the wind. Similarly landing is a problem for larger creatures as they have to know where they're going to land and how to slow down before they get to it. A lot of larger avians pick a point below where they're trying to land and pull up at the last second. Landing in water is a lot easier as they can use their feet to skid across the surface of the water and slow down.
It's important to remember that flight consumes an extremely large amount of energy. How a user of flight adapts to this can vary substantially. It is also important to note that this skill is a requirement for a being that gains wings through some transformation, but has no basis to have ever learned to use them. There are some high-powered items that instill this knowledge along with the transformation. But these are very rare.
The novice of flight is something similar to a chick that had just been forced out of the nest for the first time. They will be shaky on both take offs and landings and it may be even harder on some depending on size. They will be inefficient with their energy use and find themselves getting tired quickly. When first starting out flying someone won't know anything about wind currents and how to ride them so it's likely a novice of flight will find themselves getting knocked out of the sky a fair bit and are advised to stay closer to the ground. In addition a novice of flight will have trouble in higher elevations due to not being used to the air pressure and will have trouble flying all the way up there in the first place.
Someone who is competent in flight understands the basics when it comes to seeing and riding an air current. They aren't the most graceful in the world but take offs and landings are no longer a problem. Higher elevations are still a problem but they will find themselves being able to climb higher and higher as they get used to those heights. Similarly someone competent in flight will have stronger wings that are able to use less energy and a knowledge of air currents that can help them to be more efficient with that energy. Powerful winds can still be a problem.
An expert of flight is someone who demonstrates an acute understanding of how the wind moves, its patterns, and how to best use that to their advantage. Higher altitudes will start to become less and less of a hassle and stronger wings means the ability to contend against stronger winds. An expert of flight is always graceful when they land or take off, knowing exactly how to move to reach their mark. Experts of flight may start to find that the pressure of height doesn't bother them as much anymore and that their wings can get them a lot farther. An expert of flight will be able to go a long time without pause.
A master of flight is able to fly higher and faster than most other animals. They have learned how to use the entirety of their body to change how they fly in order to get the best results. A master of flight isn't bothered by the speed or height of the flight as they've acclimated to such pressures. Few maneuvers pose much of a problem to the masters of flight and few winds have the strength to knock them off course. They show great amounts of grace and ease in all aspects of flight and can achieve aerial feats few will ever dream of viewing let alone doing. The only thing limiting them in how long they can keep flying is how long they can stay awake or go without eating and drinking.