Just riding around will not make you faster. Just as jogging will not make you a faster runner. And descending is a skill, but it won't help your sprinting, climbing. If you are a runner and want to get faster, you do intervals that take you anaerobic, and eventually your gain speed (simply put). In order to get faster on a bike, you don't ride more miles. You ride faster miles (In short bursts gradually lengthening the bursts)and to do that you have to take yourself above your current speed to get the "growth".
As Bob said, the best and easiest way to get quicker is to ride with people that ride more quickly than you. You will struggle at first, then gain speed.
And ask any triathlete, running and cycling use muscles differently. I ride with a couple of runners who are in great aerobic shape who struggle some on a bike. Mostly because they dont know how to "gear" the bike correctly...trying to teach them. But their legs are really lean, not powerful like a cyclists. So we are trying to find a happy medium between running and faster cycling.