How do I kill a giant?
Solution 1:
Giants can't jump.
For this method, race doesn't really matter.
Make sure you have enough arrows with you. It takes about 50 steel arrows to kill a Giant, you might want to take at least 75 steel arrows with you to make up for missed arrows or slightly stronger Giants. You can farm steel arrows for free in Solitude.
Find a high enough ledge / rock to stand on in the perimeter of the Giant.
Keep firing arrows at him, make sure that you dodge his attacks if the rock is rather small.
Here is a video demonstrating how this is done, it might be considered a nasty glitch though:
Giants might be slower than you.
For this method, races that give you higher running speed and/or stamina have influence in the succes. You might also want to make sure you don't carry much with you as Weight has an influence on your running speed.
In about any game where your opponent is slower than you, you can kill the opponent by kiting it. In Skyrim, ALT allows you to sprint. You might be able to use a combination of sprinting backwards and firing arrows at the Giant for a long time (it takes longer in between shots than the other method), perhaps using potions to fill your Stamina. The problem with this method is that you might run into other opponents or against a wall, you might want to first inspect the direction in which you will run...
Solution 2:
I've been killing Giants since about level 8 as a Wood Elf specialized in sneaking and archery. It's gotten significantly easier now at level 17 but here is the basic tactics I use.
Find an environmental object that is capable of obstructing you completely from the giant's view. Stand about 20 feet away from it and fire 2-3 arrows depending on your comfort level. Do not stop sneaking/crouching and run around the rock/obstruction. Keep the obstruction between you and the giant while he looks for you. Gradually, the reticle will reduce in size until you're hidden again and he'll forget about you and walk away. Rinse and repeat until he dies.
At level 17 with ~45 archery and ~65 sneaking -- I can usually down a giant in about 8 arrows, so two or three groups of shots and hiding. When I first did it, it took me about 6-10 minutes to kill a giant (20-30 arrows). Secunda's Kiss is a great place to try it. There are two nice large rock obstructions.
EDIT: DO NOT WEAR HEAVY ARMOR -- IT IS NOISY AND THEY WILL FIND YOU EVERY TIME! Light armor only. Also, when you're away from your cover shooting, make sure you're as far away from the giant as possible so you have lots of time to get behind the rock before he sees you. Night helps.
Solution 3:
Giants are very challenging foes in Skyrim - they're actually able to take on dragons!
The best way to kill a giant is to exploit its AI. Giants are big, dumb, and relatively slow, so kiting them is the easiest way to kill them. Attack from a distance, preferrably from a place that the giant can't climb up to. Engaging them in melee combat is not suggested at all - one hit from a giant's club will kill a lower level player.
Alternatively, if there are any suitably equipped NPCs nearby, they'll take up arms against an angry giant most of the time. Try luring a giant into the attack range of a Fort or watchtower, and let the guards wear it down!
Solution 4:
Last night, while trying everything I could think of to kill the two giants at Bleakwind Basin (just outside of Whiterun), I stumbled across a trick. It's not really a glitch, just a product of the giant's large size. Not sure if you could use it anywhere else, but it works great for those two particular giants. I am currently only a level 10 or 11, with pretty low skill levels. Fortunately, this works for anyone, no matter what level or experience.
First, locate the Western Watchtower. It is directly south of Bleakwind Basin. You need to have already been there and cleared it. It helps to have a more powerful bow (I had a bow with Frost damage), but any bow will do for this technique. Try to have a lot of arrows, though.
NOTE: If you have a horse or a housecarl (like Lydia), make SURE they are out of the picture! Leave your horse at the Whiterun stable. I took Lydia up to the top of the Western Watchtower and told her to wait there. Otherwise, they will try to fight for you, and if they die (which they will), you won't be able to save your accomplishment without losing them permanently.
Get as close as necessary to one of the giants to hit it with an arrow or two. Your goal is only to piss it off enough to follow you. If you can manage to hit both giants before one of them can hit you, and get them both to follow you, great. Otherwise, you can just repeat this for the second giant. Once the giant's damage bar appears, get moving to the Western Watchtower. No need to waste Stamina sprinting, just a quick trot is enough. In fact, you may need to stop a couple times and makes sure he is still following you.
When you reach the Western Watchtower, just go through the door. Once you are inside, you're safe! The giant is too big to fit through the door, so while he throws himself against it, simply fire arrows into him for as long as it takes (it took me 14 or 15 arrows with the Frost bow). You will even get some token help from the Watchtower guards, which the giant will inevitably kill, and you can collect their belongings afterward.
Be aware: The giant will fall down and look dead, but you must shoot him at least once more to actually kill him! Make sure his damage bar disappears before going outside to search the corpse! Also, there is a sabre cat in the area between Bleakwind Basin and the Western Watchtower, so be alert for that.
Good luck, and hope this helps someone!