Hi! Great question, and there's been heaps of great answers.
My psychologist gave me a 'checklist' to help ground myself - she called it Mindfulness. When I feel detached, tired, panicky/anxious, etc., I go through the checklist & use it to calm down and focus. It's designed to use all your senses, & really makes you think about your immediate surroundings, rather than your thoughts.
For most of the steps, stand/sit still with your eyes closed & list either aloud or in your head (whichever one you feel like, taking into account where you are and such)
1. List everything you can smell. Food scents, wet dirt, even gross stuff
2. List everything you can hear. The wind, people talking, your own breathing
3. List everything you can taste. Even if it's just your spit, taste of food/drink you just had
4. List everything you can physically feel. Clothes on your skin, feet on the ground, the chair you're sitting on
5. Open your eyes & list everything you can see. People, colours, objects
Hope this helps :)