Meditation. I use a very simplified version when required and it works for me. Some call it mindfulness. Luckily I rarely need it nowadays.

Find 10-20 minutes somewhere quiet. Go for 10 at first then build up.
Set a timer and then forget it.
Sit in an upright but relaxed manner
Don't close your eyes or you may go to sleep (Well, I would!)
Before starting let yourself know that you are doing this for yourself and those you care for. May sound daft but doing things for other people is more likely to succeed. And you are doing it for other people - It will make you a better person to them.
Start to breathe slowly and deliberately and, this is the important bit,
Concentrate on breathing.
Try to eliminate other thoughts.
You will fail to do so many times but sooner or later you will be able to eliminate other thoughts and just be mindful of your breathing.

Good luck