I learned from other project fails to sand down the boards as I go. So my hubby cut the lumber and handed each board to me and I sanded down the boards with 120 grit sand paper followed by a finishing sanding block. Luckily the lumber that we purchased was not super rough so I hand sanded everything down. Once each board was mostly sanded down we put it all together.
Since my hubby countersunk the screws I applied standard wood filler and sanded it once it was dry (about 2 hrs later). I then applied wood conditioner and about 30 minutes later, followed by 1 coat of stain and 1 coat of polyurethane finish. Once the polyurethane was dry I sanded it down one more time with the fine sanding block so it was perfectly smooth.
I must confess: this was the second time I built a coffee table from this plan. The first time I built it I did a HORRIBLE job with the sanding & staining. When my husband and I first built from this plan it took us about 8 hours to build it. The second time it took us 3 hours.