Watch a basketball game, at any level. Notice how the best and most successful offensive player receives a pass. Compared to their less successful peers, the standout player most often catches the pass in a knees bent, hips down, body poised and ready-to-explode 'athletic ready' position. This ability to gather the ball and immediately, without re-positioning or changing stance or adjusting posture, make an offensive move, shot or pass, is the key to being quick and decisive.
Never catch the ball in an upright position. Because, in order to move after you catch the ball, you must first bend the knees and load the hips. The subsequent delay, from tall to small, is too much. A good defender, who is already in position, will out-quick you every time. The remedy: catch the ball low, and either stay low or move/shoot high, as part of a single, transitional motion. Low to high. Small to tall.
Preparation is the key. Never allow your posture to be surprised or unprepared. If you are ready, you will succeed.