Once you start getting to a higher level, net exchanges become much harder to play even if you are confident because a bad net will just result in getting killed. Even professionals usually lift instead of reply with a net. Anyway, in general there are two situations where you can do a tight net/spin: on a neutral net shot and on an already spinning net shot. When I say neutral net shots, I mean nets that are not tight, usually flat and are closer to the service line than the net. Usually neutral net shots are played most of the time since you don't have to commit to the net and much safer to play. In the former situation, you start the net exchange and the latter situation has you replying in the exchange. Generally, it is much easier to hit a good net shot if you are replying because it's way easier to spin when you are close to the net, and if you are fast enough or the opponent hits loosely you can just push, lift or kill. Either way, your goal with a tight net is too have your opponent make a mistake outright or give yourself a great situation. It is basically like going for a >80% smash. I will apply this theory to your Gloucestershire second match. At 0:55, you start a net exchange when you net his serve. This net was a great play since it brought your opponent in and he played a loose net. The problem was that you moved too far back and wasn't able to punish. If you try to net tight and you succeed, your racket foot should be on the service line ready to pounce. At 1:15, the two rallies are of you replying in the net exchange. In both of them, you end up lifting and getting it smashed on you. Like I said before, generally it is easier to reply so you could've just netted back and made him lift. Basically, just net tight off a neutral net shot when you're early, your opponent is out of position, or you're confident you can hit a really tight net shot. Then reply with a net if you are early/anticipated their net, they moved too far back after they netted, or you are confident that you can spin it so tight they can only lift or 50/50.