To increase speed with intervals plan
 

Hello all. I want to be able to naturally increase my speed on most of my rides. As well to perhaps later get back into racing.

What I want from anyone.

Are examples of ways to do interval training. more less on a road bike.

For example do i ride an hour and do 2 minutes of hard riding every 5 minutes?

like 2 mins hard, 5 easy, the hard again for 10 times?

or what is a good formula to follow

as well for the periods of hard riding, how hard is hard? should i be 100%?