Use a pole or tree for balance.
Extend your opposite arm and leg as shown in Figure A.
Swing leg under the body, while bringing the opposite arm back towards the body (Figure B).
Drive the knee up as high as you can, while bringing your opposite arm back behind your body. (Figure C).
Reverse your arm and leg swing, extending back to your original position (Figure A).
Repeat this exercise 10 times for each leg.