In spiritual progress, we become more and more selfless in our dealings with others; we feel an inner joy and peace.
Think of your mental state in the past and compare it with your present state; you will see the difference brought by sadhana.
Similarly, examine how many times in the day you think of God. How much time is spent in contemplating on Him? Find out what thoughts come to the mind when falling asleep and on waking up. That would give a true indication of the contents of the mind. These are the ways to find out spiritual progress.
(Source - How to Seek God, p.159-160 by Swami Yatiswarananda)