Well I know they make top dressers for such a purpose among others, but I for the life of me can't find a place that rents them around here. I've seen people take sand and/or top soil and place it around their yard and smooth it out with a rake or broom or something, but the results have always been 'OK' at best. On the other hand I saw somebody place some sort of heavy 'bar' attachment on the back of their riding mower to spread sand around their yard, and the results are positively amazing. Their lawn went from extremely uneven to looking like a putting green with just one day's worth of work. I was blown away.