The fundamental difference between haeds up and normal ring game is that the likely hood of their being a hand on the table is fliped on it's head.

Once the flop has come you've got about a 50 - 50 chance of having a pair each hand. Let alone top pair, two pair a good kicker etc.....

In a ring game you have to play because you believe you have the best hand, or at least because you can make your opponent believe that. In HU you have to play because your oponent has even worse rags than you do and you have to remind him of that.

KXo is an excellent hand. you can beat his high card almost every time.

It's not about what you've got, it's about what they don't have. In HU the mathmatically good hands go out the window. They're too rare

If you want to win you have to be prepared to bluff 1/3 - 2/3 of your hands as a (very) rough figure.

As suggested above, if you are regularly being left HU, you need to go practice, there are cheap table sto do it at. You can buy in some HU tourneys for just 20c.