From what I know of, there are tutorials, but no threads where members can ask on how to improve on specific things on improving their style and developing off of what they have right now.
As for being stiff in the air, I love to play around with holding/relaxing different joints in order to make my movement look smooth. Being stiff can be fixed by relaxing a few joints here and there, but you don't want to relax too much as it makes the spar look extremely floppy, your best bet is to simply see what joints are causing you to look stiff and attempt to find out what you need to do in order to fix that in later spars.
From what I've seen from that spar, you contract your elbows way too much, just play around with them a lot more and experiment with relaxing and holding and extending your elbows to generate momentum. Shoulder work is also a great thing, as you can generate a stupid amount of momentum by raising and lowering them, but you want to keep in mind that if you do it wrong, it can break the flow and look bad, I like to check how the shoulder movement flows by checking how they move while relaxed before lowering/raising shoulders to generate momentum.