There is nothing more frustrating in tennis, at any level of play, than facing a dull, steady baseliner who rarely ventures out of the backcourt. How do you beat a baseliner?
The first key is to be patient, even if patience isn't your leading virtue. Be as patient as your relentless, boring opponent. Avoid impulsive, reckless shots that defy the percentages, or you'll probably beat yourself.
Also vary your shots - your percentage shots - to break your reluctant opponent's rhythm. If he doesn't want to come to the net, tease him up there by hitting a deep ball and then a short angled shot. Use a drop shot if you can. Finally, come to net yourself at every good opportunity. Take the play away from the baseliner. If you take command of the net, he must hit an excellent passing shot or lob to beat you. And you have more chances to hit winners at the net.
Above all, don't be put off by a steady baseliner. Be patient and jar him out of his comfortable pattern.