"what do you do to get stronger?"
"Ride Sally ride" phrase comes to mind. I don't just ride on the road.
Road training: try to map out a course with least amount of stop signs or traffic lights. As you get really fit, even the 30second stop will cause your heart rate to drop back toward resting rate. In fact, this is one way to gauge your fitness, how fast can your heart rate drop to the resting rate. But during training, you want to maintain the "stress level" without allowing a break. Soo find a route with least amount of stops. Also do reps on hills. Even a one minute hills.
And choose your training to help you improve in the area you are weak. Can you sprint well?
Can you climb well?
Do you have the speed on the flat?
Do you have an explosive acceleration? (need this for the crit)
Cornering ability? (also for the crit)
How is your mental toughness?
I also do a lot of work out on a trainer. Mine is a mag trainer and when I was into it I would be on it 4 or 5 times a week (cause of schedule problems) and work out on it for 2 hours each time. I had a set routine on what I wanted to do.
Spinning work out (try to improve my spinning and smooth it out, more efficient)
sprint work out
2 hour grind the pedal work out (simulate a long hard mtn climb)
...
There are several really good books on bike training. I gave away mine after I "quit" riding about 6/7 years ago. So don't remember the titles.
I knew a guy who trained on his cross bike. Knobby tires and all to increase the rolling resistance while everyone else was riding their racing bike. When he got on his racing bike, it was riding on air for him.
hope this helps.
Shawn