Just a list of thing I think might help to make a tank better but Im going to start with one word "Communication".
-If you want to do a speed run ask the healer if thats cool, the healer will probably be experienced with this but sometimes they're not or they might not be geared well to handle large pulls.
-Know your limitations, don't pull giant masses of groups then promptly die because your gear just isn't up to scratch.
-Use CDs when appropriate.
-Overestimate the amount of times you need to use flash, better safe than sorry.
-Keep constant tabs on enemies agro bars especially if dps and healers are aoeing.
-If you want to ignore a mechanic in a boss fight and just burn the boss ask the group if thats ok, kind of relates to the speed running thing.
-Let healer regain mp BEFORE you pull bosses.
-Keep an eye on the mini map and chat to make sure people haven't suddenly gone afk or are lagging behind.
Now I don't main tank but this is just from my experience levelling PLD so my tips might not be totally useful but figured id chip in.