There are a couple off the top of my head, the defense suggestion earlier is spot on. I recently had to explain base defense to a Mid 100s level player.
Other ideas would be explaining xp and how it works. Many new players expect that they would get more xp from joining a higher level players run and we know this is untrue. There is no explanation of “Max XP/XP Cap” for newer players and no real way to figure out what your max xp is without simply scrolling High level bases in matchmaking and seeing where you cap out.
I know we already have a Tip that mentions One dragon and one teammate but that is still confusing to many players. I have needed to resort to 1 Drag = 100% xp, 2 Drag = 50% xp each, 3 Drag = 33% xp each.
That is not to mention the people who still believe 70% base destruction = 100% xp gain. That is how it was a long time ago but that was changed. Players are still being fed that misinformation. I have also heard, “You need to leave a couple towers for your teammates dragon to kill otherwise they don’t get much xp” No idea where that thought came from but it is untrue as well.
Another area to consider would be Resource gains. I have been told that you get less resources from a run if you don’t kill the farms. I don’t know if that one is true but from what I have seen you get full res after 70% destruction regardless of which towers you kill. The only change to res received is if someone else hits the base before you or the player uses/transfers res during your run.
Wars : Some people believe you lose less tokens in a war if your team plays dead. If you attempt to attack an overwhelming enemy or defend against them than the team will lose more tokens than if they simply didn’t participate. I have not found that to be true either.
Not sure if these are the types of suggestions you wanted but they came to mind when reading your post.