A good flooring to install over an existing floor is rigid vinyl core.
Flooring you can place on your old flooring.
If you currently have wood or vinyl flooring you may be able to lay the carpet over your existing flooring instead of tearing it out.
Installing a laminate floor over hardwood is a great option in many cases.
If this is not an issue you can sand off the old finish and or high spots then prepare the flooring by making any repairs or replacements of loose boards then thoroughly cleaning the floor.
A thin layer of joint compound suitable for indoor use spread over the old vinyl floor will patch up any gaps or dents and the holes left by removing the broken bits of the old vinyl floor.
In most cases you can install vinyl flooring on top of existing flooring.
For one thing if you ever want to revert back to the original hardwood you can simply pull out the laminate and the old floor has suffered no damage.
Things needed cleaning supplies vinyl tile cutter vinyl tile adhesive trowel floor roller.
But you can do the same to prepare your floor so the new vinyl flooring will have a perfectly even surface to adhere to.