I think the single biggest thing He's taught me so far, other than He's real and Jesus is the only way, is the importance of parents in their Childs life, and the responsibility God put on us to love, raise, teach,and guide them towards Him and teach them about life in general. I fell into the normal trap this world's laid out for us, sent the kids to school to learn, then sit them in front of the TV so I can get the rest of my stuff done at home and to get a break after work. So basically I was letting the School and the TV raise my sons. I don't know if you've seen TV or know what they teach our kids in school, but they're not full of Godly lessons. I said this on here before, but I remember before my regeneration walking in the front door to be bum rushed by both boys trying to show or ask me something, and met them with "I just walked in the door, give me time to put my stuff down and unwind a little first". This usually resulted in 2 sad children walking away with their heads down. God repaired me though, all glory to Him, and rearranged my understanding, heart, views, and priorities. Now I WANT to go see what they wanted to show me, and know that is my responsibility to teach them, not the Schools, or TV's. Now I don't even have a TV in my house, and both boys have benefited SO much from me listening to Gods direction. This has also made a big impact in my relationship with my wife as well.
To sum it all up I would say the best thing God taught me is the responsibility He's given me in my role as a father and a husband.