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.
From The Waves, by Virginia Woolf:
How much better is silence;
the coffee cup, the table.
How much better to sit by myself
like the solitary sea-bird
that opens its wings on the stake.
Let me sit here for ever with bare things,
this coffee cup,
this knife, this fork,
things in themselves,
myself being myself.