I recommend Mike Eastmans' book -- Elk Hunting the West. It has a complete section with general descriptions of typical characteristics to look for in the different class bulls. Plus it has great pictures showing the differences as well. I was fortunate to shoot a 393 bull a few years ago and it was really fun to read back through his book after that hunt.
I personally always look at a bull above the 4th point first. If it is a quick glance and his tops are good he should have good bottoms. Not always of course but it all depends on the time you have to look at them.