If you're preserving your finish:
1. Clean up your desk, dresser, or set of two bookshelves used back to back (whatever you may have found that suits your kitchen or den) appropriately. You want to ensure the furniture you are using is the correct height. For an example, you don't want to lean over your center workspace.
If you're looking to preserve the wood finish and like the color of the stain, I recommend Murphy's Oil Soap and a clean, absorbent rag. Mix according to the package directions. If you want a brighter shine, adding a tablespoon of lemon oil (per gallon of the oil soap mixture) will certainly do the trick. While, if you're looking for antibacterial, go for lavender oil instead. I do not recommend using both
*Always remove debris from the wood prior to washing it down.
2. Measure the surface of your piece. At this point you'll want to select your unit of measure and keep it standard while you work. This will help to reduce simple math errors and headaches.
3. Decide on your "topper." You have several options for a solid, easy to clean workspace here. If you're inclined to do your own woodworking, making a large cutting board topper can be a rewarding experience. If you're interested and have the supplies try this.
You can also purchase countertop or butcher's block and cut to fit.
4. Make sure the back of the piece is finished. Usually the back part of a dresser or bookcase will have a thin backing. You will likely want to select a wood and finish to the approximate color of the wood already in your piece. You may have to mix colors to get the desired depth to match your piece.
5. Add hardware, if doing so. You can, at this point, customize your piece more completely. Just using an interesting set of drawer pulls will liven up your piece. As pictured above, you may wish to attach a holder of some kind for paper towels or a dish towel dryer, while cup hooks work well to provide hanging space. You may also choose to add wheels at this point. (always install appropriate weight bearing casters to your piece and ensure they will not damage your kitchen floor - if this is possibly you may want your island on an area rug to avoid damage).
If you're painting:
A. Sand off the old paint or varnish. It is important to remember to wear a mask if you're sanding down paint. If possible, this should be done outside. **Old paint can contain lead and breathing the dust can cause poisoning.** I also wear gloves when I'm sanding.
Tips: Always sand in the direction of the wood to avoid unattractive scratches. Apply even pressure as you sand, and work at a comfortable horizontal angle whenever possible.
B. Clean the sanded piece using tack cloth to remove dust.
C. Select your paint or finish and follow directions on the product to ensure a smooth, even coat.
D. Follow steps 3 through 5 outlined above to finish.