Polarising filter help

Hi,
I impulse-bought a polarising filter the other day as I have seen them used with great effect but am having trouble working out the correct way to use it. Below are some pics I took today, one seemed okay but the rest look as though it was only working on one half of the picture.
Very uneven sky:
More uneven sky:
Same position but seems okay
Am I standing with the sun in the wrong place, do I not have the filter positioned correctly, what am I doing wrong??
Thanks,
Elena
I impulse-bought a polarising filter the other day as I have seen them used with great effect but am having trouble working out the correct way to use it. Below are some pics I took today, one seemed okay but the rest look as though it was only working on one half of the picture.
Very uneven sky:

More uneven sky:

Same position but seems okay

Am I standing with the sun in the wrong place, do I not have the filter positioned correctly, what am I doing wrong??
Thanks,
Elena