I was a Web Development undergrad, so I understand first hand where you’re coming from except that I didn’t decide on planning school until I was out of my undergrad a year. If your school has an urban studies department, I would check that first. If there is any kind of course on the history of your city, that could also be very helpful. Many students make the transition from Geography to Urban Planning and those courses could be helpful as well. Since we deal with a lot of the ills of society as planners there may also be some courses in the sociology department: demographics or anything that teaches you to use census data and quantifying it would be helpful (especially a statistics course. You don’t want to be taking stats for the first time in grad school), as well as social problems courses. I’m seeing more and more social workers going into community development so there’s some things to consider there. Likewise, you can get a little more specific if you say, felt that you wanted to do economic development instead and took some intro finance courses (many economic development concentrations have course offering for local government / nonprofit financing).

I’d recommend reading at the minimal Jane Jacobs’ “The Death and Life of Great American Cities” and if you have the time, Lewis Mumford’s “The City in History” which is a fantastic read. After that, take whatever time you have off between when your undergrad ends and grad school begins, give yourself a crash course in planning. I went through a bunch of materials on the MIT opencourseware site, lectures, saw what the assignments were like, and it shows you what books to get so if you see something that’s interesting, you can pick it up. Some of the good planning books used aren’t recent and can be picked up for a very minimal cost. Throughout grad school I spend more less money than one year’s worth of books in undergrad. But you want to familiarize yourself with the concepts and learn the names of people like Daniel Burnham, Robert Moses, Ebenezer Howard, Le Corbusier, etc. You’re going to start off grad school with groups of people who have been planning undergrads. Some of them might already hold an advanced degree or a JD. Don’t be intimidated, show up ready to impress people. Your peers and your instructors will respect and value your opinion because of it. Plus it will just make your work better overall.