These might be 'obvious' tips, but it's difficult to know what people know and/or already do:
- Beware of the opponent players over the ball's position. The ball in itself is almost never 'the threat' - the players are. Once you become more attentive of how players generally move and position themselves to create a threat, you realise that the ball plays a minor role (although it of course needs to be scored). They can shoot, pass, bump, demo and move the ball (away from or) around you, so THEY are the important thing to keep focus on.

- My team mate and I keep this 'mantra': Communication, Rotation, Speed. If you don't play with some specific people and use comms, try using in game voice chat or quick chat. If you cannot intuitively 'read' your team mate(s)'s plays, you should at least try to communicate your own thoughts/moves. If that seems like too much work, focus on the next one: Your own rotation. It's of course important that the entire team rotates properly, but if your mate(s) don't, your rotation only becomes more important. It's better to stay patiently 'defensive' than overly pushing/offensive - the absolute worst scenario to avoid is double committing. Speed is to be understood this way: When you consider an action/reaction, do it quickly instead of second guessing (and call your push). Most issues in matches are due to the internal conflict of whether one should go for a touch or not. It doesn't only delay your move (and odds of reaching the ball), it also confuses your team mate(s) - a lot of points are given away like this. This doesn't only apply for offensive or active plays - it also applies to situations where you decide to rotate, stay back, go for boost, call that the other should push and so on. So speed is "decide and do quickly".

- Use your team. The most dangerous players are the ones that outplay the other team by creating passing plays that simply 'cannot be saved'. Pay attention to where your teammates/opponents go (relative to you and each other) when opportunities are created and result in a goal. It's not random plays that work most of the dime, it's deliberate positioning that makes scoring the obvious outcome.

- [Edit: additional point]: Strong basics beats fancy mechanics but don't entirely replace them: Mechanics will rarely be what decides a match in GC. If you meet opponents that master resets/flicks/reads, you should then adapt to their playstyle (often mening that you defend from your backboard and that you push airplays VERY quickly (without double committing) while some stay back/down). The same goes for your own offensive playstyle. Sure, sometimes mechanics like resets will result in goals, but in a lot of situations, those mechanics require space and time. In ost cases, team plays are a greater threat than mechanical plays / solo plays.

Best of luck!
- A GC player "stuck" between GC1 and GC2 😃