This is a very basic way of grounding and centering yourself, using both the energy of the earth and the energy of the heavens.
Turn inward and begin to feel yourself standing by a tree. It may be a tree that you know in real life, or a tree that just comes to your consciousness. Feel your back leaning against the trunk of the tree and your feet among its roots. As you inhale, begin to draw in the energy of the earth through your root chakra and into the center of your body, wherever that may be. As you exhale, begin to pull down the energy of the heavens through your crown chakra to your center. Continue taking in earth energy with every in breath and cosmic energy with every out breath and begin feeling those energies mingling at your center.