In my son's first ever U10 tournament his last match of a round robin (where he'd lost the previous 4 matches) was against the eventual winner. He and I had no idea who was who so I just said go out there, play your best and have some fun.
Turns out he gave this kid the toughest match of the tournament taking him to deuce in all but one game, mainly because my son can handle pace very well. A big lesson in not making assumptions as different playing styles can throw up weird results.
5 months on he now knows who is who but I take the approach of not telling him what to do but what are the right questions to ask.
Even though I got beaten last time by this kid, was there anything I thought they were weak on? Where have I improved since I last played them and can I use this? What about the conditions? For a new opponent are they left or right handed? If I've seen them warm up what shots did they hit more sweetly? What is their 1st/2nd serve like?