I'm not a writing professor, but I've always thought of tight writing as clear, direct and smooth. When reading it, you don't find awkward pauses or breaks, it just flows through your head to the point that you forget you're reading at all. Unless you have a natural born talent for writing, it's not easy to achieve. By nature, writers tend to be long winded and it takes thought and hard work to condense something down to the essentials. A good rule of thumb is to ask yourself how much you can remove from a sentence while still keeping its original meaning. If it doesn't add anything; dump it.