Mindfulness practice and learning what my triggers were were the main keys to my staying grounded. Some examples:

Mental grounding

* Take a special note of your surroundings and how much time has gone by since you did "this or that".
* Visualize a calming place that you’ve been to in the past, especially during a period you felt grounded.
* Reorient yourself to the current place and time.
* Pick your music/background noises right (to avoid more harmful feelings/daydreaming).
* Prepare for a stressful event in advance using deliberate visualization and planning how you WANT to react in various situations.

Physical grounding

* Use your 5 senses to keep yourself in the moment. What do I currently "smell", "taste", etc.
* Be aware of your breathing and the feel of the air coming in and going out.
* Drink a sip of water, or other drink and be aware of your swallowing and the feeling of it.

I also like to ask questions like "So what is this day about? What am I trying to (or want to) accomplish today?" With this in mind, it can even be good to keep a "To Do" list and cross things off as you do them or create a general outline of what you plan to do and accomplish.

Writing was/is also a very grounding task for me. Not just at places like this, but on my blog.