The idea behind prot leveling is fairly simple. A prot paladin is harder to kill than one your own family members. You (hopefully) have a ridiculous amount of hitpoints, as well as armor and damage mitigating factors working in your favor eg. block rating, dodge, parry, etc. 

Basically with blessing of sanctuary up, you're not taking (WoW Gold)that much damage from anything. On top of that, you have heals, shields, lay on hands, seal of light, judgement of light, potions, bandages, and of course the ever present option to bubble hearth. This makes you about as tough as a coffin nail in thrall's cairn. When you work at leveling as prot for a while, you tend to find out the limits to your abilities and can therefore end many fights with over 80% hp and 80% mana if you work out judgement of light, and judgement of wisdom properly =D

Retribution Aura - The most simple (WoW Gold)and probably one of the more important parts to this guide. Retribution aura is your friend. Basically it's like a never ending thorns on yourself which is seriously impressive. Always have retribution aura up so that any mob that hits you will be taking damage. You'd be surprised how fast 20 dmg every time you're hit adds up.

Blessing of Sanctuary - At level 60 it reduces damage taken from all sources by up to 24 for 30 minutes. It also does 35 damage to any target the paladin manages to block an attack from. In layman's terms, this ability reduces all the damage you take, EVERY HIT AND SPELL, by 24. When you've got 10 mobs on you each hitting you every 1.5 seconds you're talking about some serious damage mitigation ok? :D 

As well as that, if you keep up Holy Shield and have some decent block rating, you're going to be doing a great deal of holy dmg to each and every person you block an attack from. Considering your 1h weapon is there purely for you to be hitting a judged target with seal of light, your shield is you main dmg dealer.

Righteous Fury - If you have(WoW Gold) specced to improve this in the protection talent tree (you should... do it... do it now...) you should be reducing all your damage taken by 6%. Hell to the yes. Along with your sick armor, block rating, blessing of sanctuary and righteous fury you can maximize the reduction in damage taken. That way, with seal of light up your health is going up even faster and you can survive for longer and take on more mobs, god this makes me happy just thinking about it.