Mindfulness is easy to do. It can be done anywhere and requires no special equipment... just you and your breath. If you are one of those people who has woken at 3am and can't get back to sleep because your mind is busy reminding you of all the things you forgot to do during the day, then this is definitely worth exploring.
I have found it so much more successful in managing my depressive symptoms - much better than Cognitive Behaviour Therapies. CBT requires you to identify negative or inappropriate thought patterns and changing them to something positive (something which I find very hard to do). With Mindfulness, you're not changing thought patterns or telling yourself to stop thinking. You are focusing on the breath, breathing in and breathing out, acknowledging any thoughts which appear and then returning your focus on the breath. Eventually, with practice, your focus will remain on the breath for longer periods, and be interrupted much less by thoughts.
You can also introduce Mindfulness into your live in daily tasks. Something like brushing your teeth, eating, walking, chores etc...
Meditation is a another part of Mindfulness. You start with just sitting for a couple of minutes a day and gradually build it up - I think 20-30 minutes of meditation is the ideal.
The other aspect of Mindfulness is what they call the 'Body Scan'. You can either do this sitting or lying down. But lying down is best. It involves listening to a guided meditation where you acknowledge how your body feels from your toes right to the top of your head. It sounds a bit odd but it's a great way to relax. I still do a brief body scan at bedtime when I'm sore or having trouble getting to sleep. I don't usually make it past my ankles before I'm snoring like a baby. It's not really the goal to fall asleep while doing a body scan, but hey, if it helps me get to sleep especially when I'm in pain, I'll take it.
There are lots of free sources out there on the web. Or better still, find a practitioner and teacher in your area and attend a workshop. After a couple of 2 hour workshops with Mike Kewley, I completed a 6 week online course which introduced Mindfulness into daily life. The tutor was based in Sutton, Surrey and she shared videos, audio files and notes from her class (there were maybe 20 people in her studio in Sutton and a handful of us online).
So if your monkey brain is a chittering pain in the ass or you need to relax your body and mind, give it a go.