Consider a Wood Conditioner
Some woods absorb stain unevenly, which causes dark blotches to appear. Birch, maple, pine and cherry can all play this ugly trick on you. It's hard to eliminate this effect, but you can limit it by applying a wood conditioner before staining. Conditioner also prevents wood's end grain from absorbing more stain than the face grain. Get a quart at a home center or paint store.
Renew Woodwork Without Refinishing
If your stained and varnished woodwork is looking a little shabby, you can save time and money with this quick fix. You don't have to strip the finish from your dingy woodwork. Just head to the store and pick up wood stain that's a close match. We like gel stain for this fix, but any wood stain will work.
Start your renewal project by washing the woodwork with soapy water. Rinse with clear water, then gently scrape off any paint spatters with a plastic putty knife. When the wood is dry, dip a rag into the stain and wipe it over the wood. Bare spots and scratches will pick up the stain. Finish by wiping the woodwork with a clean cloth to remove the excess stain. After the stain dries for a few days, you can add a coat of furniture wax or wipe-on poly to really liven up the old wood.
Better Brushes are the Key
Usually, a brush is the best tool for applying polyurethane. For water-based poly, a synthetic brush (such as nylon or polyester) is best. For oil-based poly, use a natural-bristle brush. In either case, plan to spend more for a good-quality brush. Quality brushes hold more finish, lay it on smoothly and are less likely to leave lost bristles in your clear coat. If you clean your brush immediately after use, it'll serve you well far into the future.