Are you the type of player who has trouble with focusing on the ball? Do you own a couple of tennis balls? Maybe a felt marker? Next time, draw a couple of markings on the ball (e.g., letters, numbers or symbols) about 1/2 an inch in size and rally until you can pick up the marking (coach or practice partner feeds so that you don't know which ball is being used). Guess wrong run a sprint!
With a fast moving object, the sense of sight is the most important. Train your tennis hand to eye coordination by focusing on the ball until you can spot the marking right off the opponent's string bed. The sooner you see the ball, the earlier you are able to anticipate the trajectory if the ball and prepare for it; the earlier you can prepare, the better your chance of getting in position and doing something effective and proactive with the ball. This is a great way to practice ball control. Remember, that tennis requires the striking of a moving object, with a moving object while you yourself are in motion (anticipating your opponent's future positioning is another component of motion). Or, in medi-geek: "[t]he human visual system must perform complex visuospatial extrapolations (VSE) across space and time in order to extract shape and form from the retinal projection of a cluttered visual environment characterized by occluded surfaces and moving objects", The neural correlates of visuospatial perceptual and oculomotor extrapolation (Tibber M, Saygin AP, Grant S, Melmoth D, Rees G, Morgan M.). Therefore, given the pace of the modern game, you simply cannot afford to have "lazy", untrained eyes.