I once read a book on Zen that gave the following meditation:
Sit comfortably. Breathe slowly, in through your nose and out through you mouth. With every breath, count a number in your mind. Think only of that number for the full inhale and exhale. When you reach 10, start again.
The book said many want to race past simple breath counting, viewing it as the kindergarten of Zen meditations; but in reality, it can be the only meditation ever needed.
I practice breath counting every day, usually when I wake up, before I start working, and then later whenever I realize I’m getting distracted.
I find it to be a nice gateway to mindfulness.
So, once I get to 10 however many times, I’ll let myself start to breathe more naturally, and just be aware of whatever I’m perceiving or considering for however long.