These are just some general tips that will help out any player who is considering learning to tank or has just started recently. They may seem obvious but since playing something that isn't a WAR/PLD I'm amazed at how very little of the community actually do this (obviously exclude raiders).
Original: www.eorzeaendgame.com/viewtopic.php?f=16&t=72
Paladin Guide: www.eorzeaendgame.com/viewtopic.php?f=16&t=49
• Before every pull make sure to quickly look at your party members. See if they're moving and ready to go, don't just assume that because nobody has said anything everyone's there/ready.
• Mark the initial mob that you're going to build enmity on. You don't need to mark all of the mobs, but marking 2 is sufficient. Make sure you bind your marking abilities to easy access keys. I personally use a Razer Naga, so have plenty of buttons on my mouse.
• When marking mid-fight, choose mobs that are near the melee to make target transitions quicker.
• Watch the healers MP! This doesn't mean you need to stare at their mana bar for the whole run but make sure to glance at it before pulling.
• Use your cooldowns appropriately to alleviate healer stress. If you know you're going to get hit with a large amount of damage or the healer is running low on MP don't hesitate to pop a cooldown.
• Dodge the red zones as much as you can! This may seem obvious but many tanks don't bother. (This is more specifically for non 50 tanks)
• When dodging a red zone, make sure to position yourself back to where you were originally (unless there's a void zone on the ground). That way the DPS won't have to realign.
• When tanking a boss or bunch of mobs, face them away from the party. This reduces the chance of cleaves, frontal attacks, etc from hitting the rest of your party.
• When you become more confident at tanking and taking lead of your group you can start to do bigger pulls. This is entirely group and gear dependant though.
• Check to see if you have Regen still ticking on you before a pull. Having it tick between using your first abilities can sometimes pull threat off of you.