Soft woods, such as fir and pine, absorb stain unevenly, resulting in blotchy color. Soft woods need to be conditioned or sealed. To make the sealer, thin the polyurethane by 20 percent with paint thinner. Apply it with a brush and sand it lightly when dry. If your wood does not need filling, you can go ahead and stain.
Stain adds character to woods.
It also camouflages defects and it can even make one wood look like another. Rich dark woods such as mahogany, cherry, teak and walnut are generally not stained. The final choice is yours. If after testing you decide you like a certain stain on a certain wood then go ahead and use it. Just remember to test it first.