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, featuring part 1 of "Leaves," by Lloyd Schwartz.
Every October it becomes important, no, necessary to see the leaves turning, to be surrounded by leaves turning; it's not just the symbolism, to confront in the death of the year your death, one blazing farewell appearance, though the irony isn't lost on you that nature is most seductive when it's about to die, flaunting the dazzle of its incipient exit, an ending that at least so far the effects of human progress (pollution, acid rain) have not yet frightened you enough to make you believe is real; that is, you know this ending is a deception because of course nature is always renewing itself— the trees don't die, they just pretend, go out in style, and return in style: a new style.