For me, He has manifested Himself primarily through people. I am astounded when I hear God's voice spoken through the mouths of His children - through the kind word of encouragement when I need it most, the perspective offered when I am seeing things through a haze, and the loving phrase whispered in my ear by my fiance when I am finding myself unlovable. It is in these moments that I feel I am closest to God, and they usually happen when I am looking for Him the least.
Little by little, we can build the Kingdom of God on earth by doing the very best we can with our imperfect selves. After all, as the Lord told St. Paul, "My strength is made perfect in weakness" (2 Cor. 12:9).