I do a little research before picking up the character, such as looking at videos, reading forums, looking at hitboxes and frame data, and etc to get a synopsis of what the character is capable of, the type of style it should be played, and the tools he/she has.
Then I hit training mode and test out all normals and specials. Identify which can be used for anti air, what are their cross ups, how good is their throw, do they have a kara, what can combo and what are their combos, learn a basic mixup.
Then hit online, see where I struggle, what are my tendencies, watch match videos of other players to compare to how I play the character, go back to training mode.
Process repeats for a long time until I decide to either drop the character, or keep working on him or her.