Apply tape on top of the carpet along the edge with the widest painting tape available, usually 2 to 3 inches, depending on the brand. Apply it so 1/8- to 1/4-inch is loosely taped up the baseboard as well. Then push that part of the tape under the bottom of the baseboard with a flat tool such as a spackling knife. Tucking part of the tape under the baseboard protects the carpet closet to the wall.
Add a row of newspapers, if desired, to give you a wider area on which to set your paint can and other painting tools. As you install the tape in Step 1, also tape down a row of newspapers. One edge of the tape will then be under the baseboard, and the other edge holding down the newspapers. You can also use a drop cloth.
Take apart an old set of metal blinds, cover the holes with tape and slip each slat under the baseboard and on top of a drop cloth to protect the carpet next to the baseboard and hold down the drop cloth. If the slats are not adequately holding down the drop cloth, take the cord from the blinds and insert it in between the slats and baseboard, leaving one end exposed so you can easily pull it out once the paint dries. A screwdriver or spackling knife will help get the cord under the baseboard.