If I am riding my bike to run errands, I'll just putter along. But when I break out my road bike, my goal is fitness, so I tend to try to get as good a workout as I can. I usually ride 3 days per week, Monday, Wednesday, and Friday. Mondays and Wednesdays I ride 70km on a closed cycling course at a large park. I use Strava to measure my speed, distance, and effort, and as the season progresses, I push a little more each week. I normally ride at a higher cadence, no matter what gear I use, I'm most comfortable at 90 rpm. On Fridays I do my long ride, between 130 and 150 km, riding along the river out to the countryside. I keep up a hard pace because I have to be back in time to meet my daughter's school bus.
It's not very complicated, the old saying is "If you want to ride faster, all you have to do is ride faster." I normally takes me about 45 minutes to fully warm up. At that point I mix in some intervals, that is, I pick up the pace for a few kph for a few minutes, then slow down until I catch my breath. I then repeat this a few times during the ride. Oddly, on my Friday rides, I find I'm able to ride fastest in the final 20 to 30 km, mainly because I am rushing across the city, and if I go fast enough, I can time most of the lights.