The Space Marine Rhino is a brilliant bit of kit - it's a mobile bunker that's pretty surviable under the 5th edition rules and for the low, low price of 35 points it's an amazing force multiplier. However, there is one rule about the Rhino that I always, always forget - the repair rule. So, in lieu of shooting you can attempt to repair an immobilised Rhino, succeeding on a '6'. I forgot this rule yet again last night, although it wouldn't have had any impact on the actual outcome of the game. However, it's good to get in the habit of using this rule so that you remember it for when you need it for that last turn objective grab/tank shock or even just to keep it alive in case you get another immobilised/weapon destroyed in a kill point game.
What I'm going to start doing in future is make some notes in the stressfree quiet before the game starts of things I might forget once battle is joined. So I always forget Rhino repair, Andy always forgets to fire his storm bolters on his drop-pods. These might not make huge differences but in a close run game you never know.