Fix yourself in a comfortable position.
Grounding yourself before a spell casting is a way for Wiccans to connect one's own energy with the Earth. The belief is that one can connect with the Earth and the Universe through meditation techniques, harnessing power without having to exhaust one's own energy or absorbing too much of the external energies as well.
Our technique for grounding would be to sit in a comfortable upright position and visualize oneself growing roots towards the Earth from your feet or body and from your head growing energy branches to the heavens.
Imagine the power flowing in and out of your body from the top and bottom, stretching out into the Earth and skies.
This can take as little as 5 minutes to as long as an hour. Whatever works best for you.