Peter Read's "The Black Book"
Based on heart rate, not power, but have a read anyway. And it's really old, so a more modern book might have better training methods in it.
If you want to improve a bit you can build into your ride intervals where you hit a higher average pace than the rest of your ride. Try 2x20 at 150% of your normal pace, with a 10 minute rest of 50% of your normal pace, for example.
Running training is all based around pace. A normal week running training is usually : 1 long run at endurance pace, 1 shorter tempo run, 1 or 2 interval runs and 1 or 2 short recovery runs.
So, you could apply the same where your endurance ride is a long 100km to 200km ride, your tempo ride is as fast as you can sustain for 2 hours and intervals are hill repeats: find a hill, ride up it, freewheel down, repeat (straight away) until you can't turn the pedals. Recovery rides are very slow.
Some ideas there but to improve a lot (say for 10m TTs) you will need at the least a turbo and a heart rate monitor. To really do it properly you need a power meter. The most important thing is to vary your pace and not just stick to endurance pace for all your rides.