Clothing plays a huge role. There is a reason why serious and even not so serious riders always wear cycling shorts. Cycling shorts have a chamois that covers the seams and the tight lycra is slick and has no areas that will bind or get caught. The cheap shorts are fine for rides of less than an hour, but you really need the higher end stuff if you go for closer to 2 hours or more. Performance century or elite shorts are good values.

Also, saddles with a rough surface cause chafing where a smooth leather surface will not. You can also use some kind of lubricant on the inside of your shorts. Bag balm works and so does Assos cream and Chamois Butt'r. Good ol' vasoline works fine too.