Replying to I'm bad at rails, help?

So I can slide a box without trouble but when I get to the end I can't go forward again, I always slide out switch. Like I feel myself turning backwards halfway in the box and I can't control it. Any help on that? It also may be because I am using my cousins line stepups from I believe 2010. They are built like a skateboard and weigh a ton. Also any advice for skinny features and rails I feel like a slip out easily on them just trying to slide them and I have the same problem with constantly landing and going backwards. Help is appreciated!