I've beaten him before on an older game, but this time I'm using light armor and his fire attack kills me in two seconds. This is like impossible. What do you guys do?

Fight him in less open terrain. Use rocks/trees ect to take cover from his attacks.

Time your block bashes to interrupt his breath attacks.

Use wards to negate his breath attacks.

Use Resist Fire/Magic potions.

Use lightning enchantments/magic to stop him from using shouts *because dragon shouts use magicka for some reason...*

Also, if you see the sky going weird, it's about to rain fire and brimstone. When that happens, use Clear Skies.

These are good points for any old dragon, but he is talking about Alduin, at the Throat of World.

Resist Fire/Magic potions are a must.

If you have way of staggering, or interrupting his attacks, they are immense help.

Use atronauch scrolls.

If you have Sanguine Rose, it could help.

If you can, get fortify healing rate and/or magicka rate potions.

Did you grab Dragonsbane from Skyhaven Temple?

When all else fails, lower the difficulty for that one fight

Ah, I misinterpreted the title

Also, if you use a shield the Spellbreaker from Peryite's quest is a good choice since it casts a ward which will nullify his breath attacks and reduce more damage from melee attacks than blocking with a weapon. Fortfify block potions/enchantments will help as well.

The first time? Average Nord way of dealing with your enemies.

Just slammed a greatsword against his head, and then got crushed by a meteor.

wait until you're hidden by him and score a sneak attack to start things off, then just spam potions.

Because the fire breath shout counts as a spell,so that it's able to go across long distances

Before your fight, equip yourself with Resist Magic armor and potions. Activate the Lord Stone for further Resist Magic. I assume you already have the Dragonrend shout. Don't even try shooting him with arrows because he flies too fast. Use dragonrend shout, then attack him with Dragons Bane sword (available at Sky Haven during the Blade's quest). Protect yourself with the Spellbreaker shield (my character is a Breton board and sword). The dragon's fire and ice attacks/breaths are considered as magic, this is the reason why you have to equip yourself with resist magic items and potions. Good luck!

Yet the players Fire Breath shout does not use magicka. You also misunderstood my point

Only one other person mentions the only thing that renders him vulnerable to harm in the first place: Dragonrend, and not a hint of deft tactical use of it either. It is the one principal thing that enables you to beat him, and not just because of its plot-mandatory...ness.

Dragonrend has a very quick cooldown even at full power. Go in with an Amulet and Blessing of Talos and it's down to 9 seconds. Once it recharges, just use one word over and over (3 second cooldown) to keep him grounded and in a sort of stun-lock so he can't roast you with that dragonfire. Time it right and you can have that one word ready to shout again right as he builds up to fireblast you again, interrupting him. Approach with caution though, he still bites.

Depleting a Dragons Magicka Pool does prevent the Dragon from shouting, but Alduin should already be grounded. Any Dragon that can not Shout will chomp on an Opponent.

Charge Him jacked up on Soups and Stews, then spam Power Attacks.

Spellbreaker can be used to defend from Fire Breath and also used to Shield Bash.

Mages should Summon a few Distractions, and not get eaten.

But, I want to beat Him with Hand to hand!<--- You chose to do it and now must suffer for Your choices.

Frost Atronachs are very powerful Melee Summons, and Alduin should be grounded and kept unable to escape.

EDIT What Madcat221 said is very relevant to keeping Alduin Grounded and Vulnerable.

That is a good tactic. My problem with Dragonrend is that it does not work like I think it should. I blast the Dragon (Alduin in this case) and he flies about for maybe 30 seconds, breathing everywhere. Then he lands I may get 2-4 good shots at him. I Dragonrend him again and off he flies, circling for another 15-30 seconds, breathing fire. Rinse and repeat.

For a shout that supposedly renders a Dragon in fear of mortality, they sure can fight its effects for a long time before going to ground.