Forget smoothing and masking tape.
If the line looks uneven after applied, it was applied incorrectly. Secret
is to *push* caulk on, after very clean right-angle cut across nozzle with
razor. Hold the tube in both hands bisecting angle of two surfaces to caulk,
hold it almost at right angles to the caulk line but slightly obtuse angle
off vertical, so it is pointing slightly in the direction of application,
then slowly shove the nozzle forward, regulating the squeeze rate so the cut
tip passes over the just-applied buldging bead, flattening it. Get a really
high quality caulk cartridge gun - the better ones have exquisite flow
control with a big operating lever and an extra smooth operating ratchet,
and release. Squirt out caulk so that there is just enuf excess to have the
trailing side of the nozzle tip smoothe it out.
For acrylic caulk, a wet finger can be used for fine smoothing.
For silicone, you better just do it right the first time, as it is hell to
re-smoothe, and looks nasty when flattened with finger or spoon, as it is so
Also, use fresh room temperature caulk only, as it stiffens and is difficult
to apply after a fairly short time.