Have not yet read any of the other responses, will do so after posting.
Make sure that you have a primary care physician, and that you maintain a regular relationship with him or her. Make an appointment to meet your doctor and get a complete physical or wellness check, and discuss any concerns with them, now, before you develop any new problems, and talk about any current medical situations you have.
Make sure your doctor does a complete skin cancer screening.
Stop eating garbage (and learn about healthy eating and cooking) and develop new healthy eating habits. Eat more fruits and vegetables, and less processed food and meat. Eat more high fiber foods and/or add a daily fiber supplement into your diet.
Give up smoking, and drinking soda (both diet and regular) and drink more water and unsweetened tea (decaf if you are sensitive to caffeine).
Brush, and floss, your teeth every day.
If you have dental problems, get those problems fixed right away. An unheallthy mouth can lead directly to heart problems, and infections of all kinds.
Read about that here: https://www.webmd.com/heart-disease/features/periodontal-disease-heart-health
Make sure to do some aerobic exercise, and strength training, and balance exercise every day. This is common sense “use it or lose it”.
Take care of your feet. Keep your nails trimmed and clean, and keep your foot skin, supple and free from cracks, and sores, and fungus, and ingrown toenails. See a podiatrist if you need to, but learn to care for your feet in a daily basis, including avoiding high heels and shoes that don’t fit.
Be a good friend to your current friends, your neighbors, and your relatives, and walk away from toxic relationships.
Be kind to animals.
Do inexpensive things that you like and love on a regular basis. Schedule in time for fun, joy, and relaxation.
Vote.
Pay it forward.