One I like to give a lot is to reflect on the dependent arising nature of our understanding, and other good qualities. This helps to lessen the idea of "me", and "mine". Say, we are getting conceited about our understanding or some type of quality we see arising in our practice, then it is very helpful to reflect on how it arose, going right back. Dependent on what, how did this arise? This is reflecting on the Sangha. It depended on us hearing the Dhamma, and this depended on others. Keep going back, to see how many people were involved in this process of us developing these qualities, so that we develop a sense of gratitude at the same time as we develop a sense of humbleness.
Another way to develop humbleness, especially if we are judging others' unbeneficial qualities, is to ask ourselves "Am I free of this quality within myself? Am I free of greed? Am I free of hatred? Am I free of ignorance? Have I got beyond this?" That will help lessen our tendency to judge others so much, and develop a little bit more humbleness, realizing that we aren't enlightened either, and that from time to time perhaps we have this quality arising in ourselves.
Another way to develop humbleness is to ask yourself, "Am I going to die?" This helps us develop more humbleness.