This is one of my favorite things to do on a box. Definitely ollie into it and practice lots on flatground. One of the keys is body position, reach your back hand out over your tail and your front hand down towards your nose or out over your nose, this will keep you nice and straight and balanced, you don't have to lean crazy forward, just have all your weight over your front foot and it helps to straighten out your back leg a bit. When you get to the end push forward with your front foot to nollie out. Its less about leaning forward then it is lifting your tail.