Summarize this article:

Start any Timberland cleaning session by brushing off the boot. Start at the top of the ankle and brush back and forth all the way down the whole surface of the boot.  If you just have a small amount of debris stuck to your boots, this light brushing will typically remove it. If there are deeper scuffs or lots of debris, you should use the brush to remove as much debris as possible before moving on to other cleaning methods. You can use any clean, soft brush for cleaning your Timberland boots. However, the Timberland company does sell a kit that is made specifically for cleaning Timberland boots. You can also get a brush that is specifically made for brushing suede or nubuck, which is usually called a "suede brush." Use a simple pencil eraser, a generic suede eraser, or a Timberland cleaning bar to remove scuff marks on the surface of the boots. Rub the eraser or cleaning bar lightly over the marks until they disappear. The eraser or cleaning bar can take care of most day-to-day scuffs and light marks. They do not work well for removing ground-in dirt or mud that has covered your whole boot. Once you have erased all marks on the boot, use the brush to smooth out the surface of the nubuck. The brush will also remove any eraser debris that might remain. Move the brush lightly across the surface of the boot, making sure to move it in 1 direction. This will ensure that the surface has a uniform look when you are done cleaning it. Keep your Timberland boots clean by removing dirt once per week. This is especially important if they are worn on a daily basis, as dirt and grime can really build up. With some weekly maintenance you can keep your boots looking fresh and new for a long time.

Summary:
Remove small debris with a soft brush. Remove scuff marks with an eraser. Brush the boot once again. Do spot cleaning on a regular basis.