My girlfriend asked me to clarify something she learned, and so I thought I’d share with the rest of you after thinking about it some more. I’ll be using yoga references as well.
When I ground myself, I usually begin in tadasana, or mountain pose. In tadasana, you should be standing straight, your ears parallel with your shoulders, and those lined up with your knees and feet. Don’t hyperextend(lock) your knees, but let your muscles support the weight. Lift your toes up, spread them, then press them into the ground and evenly distribute your weight on your knees. Begin breathing from your belly in long, slow breaths through your nose. Breathe in for a count of five, hold it for five, let it out for five, keep your lungs empty (if you can!) for a count of five before beginning the cycle again. If this feels unnatural, just breathe normally.
Slowly relax your body, starting with your toes, to your knees, thighs, abdomen, chest, and neck. Relax your mouth, your eyelids, and your forehead. Imagine, through your feet you have tree roots growing down into the nourishing earth. Find the energy, the nourishment there and make it travel up your roots, and into your body. Bring it up your legs and spine, or your trunk.
Then, on an in-breath, raise your arms slowly above your head, so they’re lined up with the rest of your body, palms facing each other. This is urdhva hastasana, also known as upward hands or upward salute. It helps relieve anxiety and center the mind, while also using your arms and hands to serve as your tree branches.
Let the energy from the earth fill you, and go up your branches. On your out breath, imagine all negative energy and stress leave your body (I imagine it leaving through my mouth, expelled with the air in my lungs) and return to the earth. All your worries, insecurities, just let it leave your mind. On the in breath, take your fill of positive energy again.
In yoga, during urdhva hastasana, we would streeeetch upwards during an inbreath (keep your feet flat!). Do so, and imagine you’re soaking up glorious sunlight, before relaxing on an outbreath.
When you feel ready, bring your arms back down to your sides for mountain pose, wiggle your fingers, quicken your breath, and if they were closed, open your eyes. 
This is the way I ground and center myself , but there are also numerous other ways, such as using your chakras, or using other elements to ground/clear yourself. For instance, burning away negative energy by imagining a purifying fire, or gently washing it away with soothing water. Just find the one that works for you.
