In order to develop single-minded devotion, the mind must be trained. It is natural for the mind to wander towards gossip, politics, sensational issues, worldly comforts, etc. When your mind wanders, draw it back to the lotus feet or the image of Bhagavan. Eventually, this tendency diminishes.
Positive qualities such as faith, patience, tolerance, fasting, satwik diet, and brahmacharya can help develop a single-minded focus on Bhagavan.