Here are the most basic steps of self-care in the form of question prompts.
Know how to deliver Emotional First Aid for yourself and for others. Make an EFA kit stocked with things you find soothing. You can even make a portable, pocket-sized EFA kit that fits into an Altoids tin.
Soothe yourself with stress relief activities for the 5 senses.
Explore the categories of coping skills with their pros and cons. Here is a list of 99 coping skills.
Grounding techniques can relieve anxiety and other unpleasant emotions.
Try some relaxation techniques such as breathing exercises and progressive muscle relaxation.
Many herbs can ease anxiety and promote calm. Consider aromatherapy or dreampillows if you're not into herbal tea. Note: if you have issues with intrusive memories or a fresh trauma, do NOT use rosemary, which enhances memory. Save that to study for tests or address lost/fading memories.
Stressful experiences often interfere with sleep. Take extra care with your sleep.
Acute stress reaction is a normal response to an abnormal event. Most people will freak out or freeze up for a few days, then gradually recover. Treatment typically consists of common sense comforts. The most important point is to listen if someone wants to talk about what happened, but don't pressure them to do so.
Preventing PTSD is important, but caregivers are just beginning to identify things that help. First, understand that PTSD is fundamentally a sorting error: the brain can't file traumatic memories properly, so they replay over and over again. Playing a stacking-and-sorting game such as Tetris can activate the brain's sorting function. Making a care diary, timeline, or trauma scrapbook can help place memories in context as part of the life story.
Bad stuff happens to everyone sometimes. You can cope with it. You can help other people cope with it. Learn the skills to be a hero. The world needs more of those.