i'm always trying to assassinate people: sneak mode, close, and with a regular steel sword, but it always fails. it attacks normally. what am i doing wrong?

Are you sneaking? Make sure you're pressing the right button, it should say you're hidden. If you get a fully open eye it means you're detected. More importantly, do you get a 2x damage multiplier? If you do get it, then the enemy is too strong to die in one hit.

You're not doing enough damage. That's a finisher for when your sneak attack is strong enough to kill in one strike. I don't think it occurs every time, either.

i am sneaking, and what button is it in the 360? the regular attack button? and i get a 3x multiplier

It is supposed to attack normally. The assassination is a kill animation. You need to do enough damage in one attack to do critically damage them and even then it is still random whether or not you get the animation. Pump up the right side of the sneak skill trees to up sneak damage for either 1-H or Daggers. I've only done the animation a couple times on my stealth build

Will it work if you do a dual power attack with daggers? Is there a separate animation for that, or nothing at all? I haven't gotten my sneak high enough yet.

You don't need to do any damage. There was plenty of times I snuck up on people and assassinated them without lowering their health 1st. Just remember it doesn't happen every time and you need to be in sneak mode once you attempt it.

the elvel 50 sneak perk for 15 x damage to daggers will really get this done combine it with a high one handed skill and you wont be disappointed

I actually do it with sword/dagger.

Do you do it by holding both triggers down? Or just tapping both? Or by using just your dagger hand?

Well I've done it with the sword. I just attacked with my main hand. Just got the 15x dagger perk so now I just use a dagger. Haven't gotten the animation with it yet because I've only used it against skeletons

It works with dual daggers, but you don't always get the animation, even if you one-hit them.

can u do sneak attacks with a 2h weapon?

I've only got this to work with a 12x multiplier and a single dagger. Of course sneaking and being undetected and all that.