What you need:
Random Orbital Sander
Sanding discs for your Random Orbital Sander (at least 180 & 220)
1 clear 1 qt calibrated bucket.
1 can of Oil Modified Water Based Polyurethane.
3M between coats finishing pads
3M final stripping pads
3M final finishing pads
1. Sand your surface in successively finer grits down to 220 grit with a random orbital sander.
2. Spray the surface with water and allow it to dry. This will raise the wood grain. Don't skip this stage!
3. Sand your surface to 220 grit with a random orbital sander, to remove the raised grain. This way the grain wont raise again after you apply a water based polyurethane to the surface.
4. Open the can of water based polyurethane.
5. Using a scrap piece of wood, (dowel rod is perfect for this) stir the Polyurethane. Stir from the bottom up to re-introduce the sediment to the polyurethane.
6. Pour as much as you think you'll need into a clear 1 qt calibrated bucket (Home depot sells them for $0.99 each).
7. Using either a paint brush, a foam brush/pad or a soft lint free cloth/rag (best in my experience), give the surface its first layer of water based polyurethane. Once you're done, It wont look great, (lots of brush, sponge, cloth marks and bubbles) don't worry, the polyurethane shrinks as it dries so it will look better.
TIP - You don't need to use any special, wipe on Polyurethane to wipe it on with a cloth, the normal stuff goes on just as well. I found that wiping creates less defined marks and a better finish in my experience as long as you wipe slowly, with the grain and from one end of the work piece to the other to avoid stop and start marks. Don't wipe off the excess like you do when applying some other finishes by cloth.
8. Wait 2 hours for the finish to dry.
9. Sand your surface with 220 grit on a random orbital sander, don't be to brutal though, you're trying to build layers not sand each one away. Alternatively use a 3M 'between layers' scotch pad on your random orbital sander if you want to be less aggressive.
10. Apply a second coat the same way you did earlier.
11. Wait 2 hours for the finish to dry.
12. Sand your surface to 220 grit with a random orbital sander. Alternatively use a 3M 'between layers' scotch pad on your random orbital sander if you want to be less aggressive.
13. Apply a third coat the same way you did earlier.
14. Wait 2 hours for the finish to dry.
15. Sand your surface to 220 grit with a random orbital sander but this time, make sure that you remove all valleys and peaks in the finish so no dark patches. If you sand through to the wood in any area (check) apply more coats, but at this stage you probably wont need to as long as you don't go crazy with the sanding.
16. Place a 3M 'final stripping' pad (scotch pad, available from Lowes) on your random orbital sander (don't worry, it will grip and spin). Rub out the finish thoroughly (about the same amount of time as it would take to sand the surface).
17. FINAL STEP - Place a 3M 'final finishing' pad (scotch pad, available from Lowes) on your random orbital sander. Rub out the finish thoroughly.
The results will speak for themselves at this point.