Keep it up and you'll see improvements. A lot depends on your goals, whether you are trying to become a faster rider, more endurance riding, or simply stay fit. I have found that my biggest improvements in cycling have come from riding regularly and doing longer rides on weekends.

I have found that setting goals really helped me improve. I cycled a lot when I was younger, quit for a while and started back in my early 40s. My initial goal was simply to lose weight and become more fit. I really enjoyed cycling again and decided to start training for a week-long bike tour the following summer. For a while, I got caught up in the fast group ride scene and trying to continually improve my performance (eg, avg speeds). However, as I have gotten older, I could care less about going fast but I do track my mileage, time and pace.

My goals now are to maintain fitness (and weight) and keep myself in shape for bike touring. I love taking bike trips, and generally participate in several each year. To stay in shape, I commute to work most days and try to do at least one long ride every weekend. I get a lot of enjoyment out of bike commuting and a sense of purpose that I never got from recreational rides -- for environmental reasons as well as saving energy and driving expenses. Regular commuting and weekend rides keep me in great shape for bike touring, and I have no trouble riding week-long tours with no additional training. Some day I would like to ride my bike across the country.

I have also found that tracking all of my exercise (mileage, time, etc.) keeps me motivated. I set weekly and monthly mileage goals for myself, and often that motivates me to ride on days when I might otherwise slack off. Tracking your commuting can also be a motivator.