To me, sadhana is a daily spiritual practice allowing time and space for an individual to turn inward.
As Yogi Bhajan (of the Kundalini yoga tradition) says, "Sadhana is self-enrichment. It is not something which is done to please somebody or to gain something. Sadhana is a personal process in which you bring out your best."
Sadhana could be taking a walk in nature, doing breath work or yoga asanas on a mat, spending time meditating or chanting, reading and reflecting on a poem, or simply watching the sun rise.
Please accept this post as a possible starting point for your own practice today.
Presents, by Norman MacCaig
I give you an emptiness, I give you a plenitude, unwrap them carefully — One’s as fragile as the other — and when you thank me I’ll pretend to notice the doubt in your voice when you say they’re just what you wanted.
Put them on the table by your bed. When you wake in the morning they’ll have gone through the door of sleep into your head. Wherever you go they’ll go with you and wherever you are you’ll wonder, smiling about the fullness you can’t add to and the emptiness that you can fill.