Just do it as described in the FCTM ,it works as magic!
30ft rad alt if it helps or when the runway starts to rise,pitch up to follow the runway rise motion while closing the thrust (same speed as when you adjust sthrust in flight) so that when you touch the levers are idle.
You cant go wrong, just read the books!
If you tend to flare too low ,rise your seat,if you flare too high,lower your seat position.
You should see where the wiper connects with aircraft skin.
If you float on the 300 ,you better stop it cause youll never touch down on 800
If you foat,it means either your speed is too fast into the flare or you keep the thrust too long and reduce it too slowly.