You need to sand the existing finish w/120 then220 then 400 then 600 grit sandpaper. choose your new stain and apply with a rag in 3coats stain 3coats polyurethane.
Begin with stripper if the item was stained. Then sand surface back to its natural wood. After this, begin staining using a wash cloth and repeating after drying if necessary.
Either sand or strip the wood. Use a tack cloth to get the loose particles off. Stain the wood, varnish the wood, sand lightly with fine sandpaper and varnish again.
