This is a simple but effective trick when it comes to caulking seams.
Cut a plastic bottle bottom off a Coke bottle, soap bottle, etc., leaving a couple inches of height. Fill with Dawn or your favorite generic liquid dishwashing soap.
Prepare and caulk the applicable seam as appropriate. Once a section is completed, dip a finger into the liquid dishwashing liquid and run down the bead of caulk. The excess caulk won’t stick to the soap and you can wipe the excess off on a paper towel, leaving a smooth, professional finish.
Can’t take credit for this, as it was taught to me by the owner of Bayshore Boats. But it works well, looks good and minimizes caulk waste.