Once you feel like you're properly set up on your bike, (fit is very important) you can start mixing up your rides a bit.
I'm a big proponent of interval training. To give you a rough idea of what that entails, if you're going to be out for an hour, you could try a variation of this: Give yourself a warm-up, then go flat out for maybe a minute, followed by about eight minutes of recovery. Repeat this a few times, then cool down for the remainder of your ride. Your current level of fitness will dictate the interval. When you first do it, that minute may seem really long. If you're young and really fit, it might not be so much, and you can do one in five.
Another option is to take your current distance, such as a 30 mile loop for a two hour ride, and try to cut your time by sustaining a slightly higher speed for the duration. Either way, you want to raise your intensity every other day, or every third day, depending on how hard you ride. And you absolutely must give your body at least a day of rest, maybe two, otherwise you'll get burned out, and it won't be fun.