Here's what I do when I run sub-50 dungeons.

I bind my marking macro onto maim. This means the mob I am attacking automatically gets marked when I activate maim. At the same time, I use the same button to mark any other mobs I intend to attack or when I swap targets. 2 functions mapped onto 1 button and I don't need to have 2 buttons of a similar skill on my bar. The advantage being I am able to turn on/off the mark using the same button and its really fast.

Marking REALLY REALLY helps in sub-50 dungeons. I always assume that the players are new and they need as much help and directions as possible.

I always play on the side of caution and try to make life on the healer easy. Having played tanks, heals and dps, I don't go in assuming the healer wants me to make his/her life fun by doing big intensive pulls.

Another thing I do in sub-50 dungeons before I start would be to ask if anybody wants to do a normal run or a run for experience where we clear every room and all mobs especially if I notice that there are some non-synced players.

My experience would likely be very different from you as I play on the JP servers. But I think the abovementioned are applicable regardless.

On the JP servers, the tank drives the run, the healer co-drives and the dps all defer to the 2 and just chillax and enjoy the ride. It's an unspoken rule and dps who are too zealous don't get much approval or are frowned upon.

It's very much the same with 24 man raids, there are alot of unspoken conventions such as the Alliance B tank will be the de facto tank for the entire run. Alliance A and Alliance C and their tanks will handle the fight mechanics. Nobody tries to upstage the B tank and all defer to him/her unless required to take over the role (eg. specific request, death etc). Aggro output is controlled to ensure it is never ripped off the B tank.

All these make for very smooth and fast runs even when they are not speed runs per se, because everybody simply understands and adheres to all unspoken procotols.

Not sure if its an option available to you, but if latency permits, you might wanna give the JP servers a try; it's a very difference experience I can assure you.