Tips? Run like the wind, hope for the best and expect the worst. 55 minutes is generally insufficient time to connect, given you will also have to pass through Immigration outbound (last week took perhaps fifteen minutes to clear earlier this week), as well as go through a quick security and docs check at your departure gate. Given we do not know whether you will also change from T4 to T4S, can't say much other than it will add time - and take the lifts preferably over the escalators.