I used very fine sandpaper -- you're only trying to clean the area up a tad. (Terry can correct me if I did it wrong.)
If you get the plastic ones from HD that are used to shim windows, you just snap them.
Also, if you can get a little tube of polyseamseal instead of silicone caulk, it's easier to get up later. You can also get a thing for your caulk gun of Polyseamseal, but it's going to be way more than you need. And use one of those little plastic 90-cent tools from the hardware store to smooth the "caulk" bead; makes it look way professional