Ride them again and again and again.
Focus on using smaller gears at easier cadence. Stay in the saddle as much as possible. Try doing some lower body focused weight lifting, particularly using low weights at high reps. Work on improving your pedaling form by doing form drill on flat land (in simple terms work at spinning a very high cadence 90-100 rpm) as this will improve you power efficiency at all cadence and effort levels.
Oh. and Do it again and again and again and again and again.