For a neat bead when sealing around a sink or the gap where shower wall meets tub, pull out the painter's tape. Lay parallel strips, about 3/16 inch apart, on either side of the seam, and squeeze in the caulk. To smooth a silicone sealant, which is tacky and difficult to tool, dip a finger in dish soap before running it along the span of the bead; a finger moistened with plain water works for acrylic latex caulk. Remove the tape while the caulk is still wet. One more swipe with a damp finger eliminates tiny ridges and leaves a smooth, concave bead.
Cut the caulk tube's nozzle at a 45-degree angle to create an opening that's just big enough to fill the narrow gap between the tape strips.