Mahabharat is an ocean-like great epic. There are many lessons to learn from it & to apply in our daily life to be a good human being. Here are some lessons which I personally try to absorb within me:
1) Each & every advice uttered by Lord Krishna in Shrimad Bhaagabat Geeta, & also His other advices like regarding telling lie in Karna parva or in Anugeeta. Nothing to say much here as they all are God's direct teachings for us. We must obey Him.
2) The greatness of Bhishma Dev teaches me how to control own senses, how to sacrifice whole life for others, or for a greater cause. Also he teaches me to be determined to my promise if there is any.
3) I know there are many Yudhishthir haters in this forum, but I must confess that I have many lessons to absorb from him like peaceful nature, tolerance & patience. Also, I want his truthfulness in my character. Control of anger & forgiveness (which always makes me overwhelmed whenever I read the epic) must be taken from him, in order to create a beautiful world. If I could absorb even 1% of his forgiveness, it seems to me that I turned into Goddess.
4) Bheem's simplicity & Vinashaya cha dushkritang' nature. I want to learn that pure anger towards evil which wants to destroy adharma without any compromise, but beautifully controlled by Dharma & God.
5) Arjun's Devotion & surrendership to Krishna.
6) Last but not the least, Mahabharat always tells me that, do not worry if you are always in path of Dharma, because God is on your side & definitely you will win finally.' (Yato Dharma stato Krishna, Yato Krishna stato jaya' - wherever is Dharma there is Krishna, & that side wins wherever Krishna is.) I have no fear in Kurukshetra wars of this Kaliyug life as long I can follow Dharma & be loyal to God. That is the greatest lesson which Mahabharat gives me.