Many ways to skin that cat obviously.
We change to STD at transition altitude and yes, we do brief it during our normal departure briefing as it is different at nearly every airport. However our standby altimeter remains on QNH until top of climb for a possible return. In case we have an extra metric altimeter on the classics (dont need that in the NG anymore) it is allways set at standard except when operating in metric countries.
Back down we set well before top of descent the standby altimeter is set to QNH of the destination (QFE operation is not allowed anymore), values from the ATIS or ATC. The main altimeters are switched to QNH once we get a clearance to an altitude. Of course if we get a reclearance to a FL we have to switch them back to STD.