At the very least, it should have at least one great picture of the finished quilt, yardages for various sizes, and clear, correct instructions. The most efficient methods should be used, and time factored in. If a quilt wastes my resources, it won't be one I'm likely to make.
I think most people like patterns where you can see some progress as you go along. Look through books by Eleanor Burns for examples of good, concise directions. She always finds the easiest technique and explains things thoroughly.
I have seen some that make you cut out hundreds of triangles, which could have been peiced together in less than half the time. Another thing I hate to see is a requirement for some fancy ruler that will add $$$ to a project IF you can even find it! I probably have more than a dozen rulers now, and seldom use more than a couple. And for some mysterious reason, I keep looking at the fancy new ones. When will this madness end?