One of the most common mistakes I see when players warm up or practice is to hit each shot properly, but then backswing immediately for the next shot with no move to a neutral position. In other words, if they are hitting backhand to backhand, after each shot the player goes directly from the forward swing to the backswing for the next backhand. They are practicing something they would never do in a game, while not practicing a key thing that they would (or should!) be doing in a game. If you don't do it in practice, you won't always do it in a match, and you'll get caught off guard - and often won't realize the cause of the problem.
In a game situation, you wouldn't know that the next shot is a backhand. So you'd instead move into a neutral position, ready for forehand or backhand. That roughly means your racket should be pointed at your opponent. Even in a very fast rally, you'd get into that neutral position and not start your backswing until you see where the ball is going, forehand or backhand.
So, instead of practicing a 1-2 backswing/forward swing, do a 1-2-3: backswing/forward swing/neutral position.