It may be that you can just hop on a bike and ride 30 miles without the least problem. Especially if it's absolutely level with no headwind, this is a fair possibility. But, if you do have problems, the middle of a tour is a bad place to find it out, and could just ruin the trip. So ideally, cycle enough beforehand to either get in shape or to know that you are in good shape for cycling. If you do expect to cycle 30 miles every day, be sure you've done it at least once before you go.

If you do get into riding hills, even fairly low ones, or sustained headwinds, it can really be a chore. You need aerobic fitness for that, and if you're in fairly good shape (like if you jog and stuff), then you may be all right on that part. But it's also a major workout for a few of the muscles in your legs, so doing what you can to get them in shape or confirm that they're in shape beforehand is a good idea.

I'm not an especially fast rider, but I recently did a 66-mile ride. One of the problems I had was that they expected everyone to be done by a certain time, which meant I needed to keep my speed just a little above what was comfortable for me. If you can ride at your own pace and take all day to do 30 or 50 miles, that'll help a lot. If you have a big group and they say "We're going to leave at 8:00 and be there at 10:30", that'll make it a bit harder on you.

Also check into the types of bicycles to be used. The bicycles easiest for a beginner to hop on and ride are not necessarily the ones you want on extended trips. If you furnish your own bike, you want to be sure you know how to fix or adjust most of the things that could go wrong on the trip, and have whatever spare supplies you need for it. If someone else furnishes the bikes, I would think that's all taken care of.