I'm playing a sword and board guy (Breton) on a PC and I don't think I've been able to pull off a 1-handed power attack yet.

Everytime I try a power attack I careen past the target and swing at the air. Then I have to turn around and try and find the target again. I have not had this problem with 2-handed as 2-handed power attacks seem to work very easily and are exceptionally powerful.

I've tried practicing on a training dummy, but haven't mastered it yet.

Any suggestions on how to master this?

Also, movement during 1-handed combat seems very slow and cumbersome. I find it very hard to get my guy moving forward when the target is just out of range.

I usually prefer side-stepping during my sword n' board attacks. When you move left or right during the power attack, it's like sweeping the area in front of you with a power attack. I hardly use forward movement power attacks, because its hard to guess where the enemy might move. If it's a caster who is casting...I'll do it because I know most of the time he won't budge during the cast.

Anyways, try side-stepping while doing your power attack, should get more hits

Yeah, this is because you are moving forward when you do the attack. If you are right next to the guy, you don't need to move forward as you attack. If you do a forward power attack, you need to be about 5 or so yards away.

Don't move while power attacking, it will goes out much faster.

I do "double attack trick": do a regular attack, and as soon as you begin to strike, hold the attack button, and the power attack will be almost instant after the first blow.