Not knowing what sort of time
Not knowing what sort of time you have available and what training you do at present, this advice may or may not help.
I would say that adding interval training sessions to your routine will help. They are quick and the payback is good. The downside is they hurt and you need to be disciplined to get the most out of them.
If you have ever time trialed you should have a good idea of your max sustainable power for an hour, use this to gauge your exertion level and try 2x20min intervals with a 5 min rest between and a 10 min warm up and warm down either end. You should aim to sustain your max 1 hour power for the entire interval, so use cadence etc to make sure you stay on target.
This is a good session for building sustainable high level output. One of these sessions a week should start to show improvement over time.