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how can i become better ?

I would suggest practicing leaping to sprint speed and then going fast on the flats.

I am not being a total smartass, either, although I am chuckling right now.
I really do think training for what you want to be able to do is the most effective.

how far do you want to ride "fast" for on the flat? is it just for a race, TT's or a group ride?



first thing first make sure you can complete the distance at a steady pace. so do a couple of slow rides a week about the distance you're aiming for.
then (in a separate ride) do some intervals shorter than that distance at a higher pace than you would do the full distance. 2 x 20 minute intervals if its a long distance, 4 x 5 minutes or something if its a 10 mile TT.
then in another ride work on your sprints.
done

or you could go out on group rides with a club which will push you to ride faster and depending on the group might involve some sprints. much more fun than training rides if your goal isn't super serious

Train.

It would help if you describe you actual training the last 4 weeks.

In general: One or two long weekly rides , two interval sessions pr week, one Vo2max and one FTP and one or two tempo rides. This will improve you power/ speed on the flats.