BigSteel, the best thing you can do is research. When I started I was all about finding the perfect yard plan already done, so that all I had to do was reproduce it.
As I researched and read more, I began to understand the underlying concepts behind yard operations, so that I could confidently start to plan my own.
There's an old, but still really good book called Track Planning for Realistic Operation by John Armstrong that has a ton of information on the different types of yard design.
Alternatively, you could locate a prototype yard to model. Google Earth has aerial views, but of course you have to know where to look.
I had made the decision to model Parkdale Yard in Toronto, for the simple reason that I used to live near enough to it to hear the trains shunting in the night. It was also a relatively small yard and that made it a good choice to model.
Meanwhile, my research has led me to a gentleman who actually used to work there, and he and I have been corresponding for the last month or so. He's provided me with some invaluable information and the more I learn the happier I am about my choice of this yard to model - it's perfect for me.
Anyway, like they say, research is half the fun.
Val