There are different schools of thought about graduate school: some say, "Go now while you know how to study!" and others say, "Wait until you really figure out what you want to do, then go if you need to." Indeed, many graduate programs do prefer it if you have some experience under your belt before starting graduate studies. And, because of the cost, effort, and time required, it makes sense to have a specific goal in mind when pursuing a graduate degree. It never hurts to talk to professionals in your field of interest to find out their perspective on whether grad school makes sense and, if so, when. Of course, talking to a career counselor in the Career & Co-op Center could help provide some perspective and information as well.
If, after carefully considering your motivation to attend grad school, you've decided to go for it right after completing your undergraduate degree, here's a sample timeline for researching schools, and preparing to apply for graduate work.