The videos on the web make it look very easy. All you need is a
steady hand. My problem is that I don't have a steady hand. (Want a
laugh? You should watch me eat with a fork)

I saw this tip on the web and considered trying it, but I can't
imagine how I would pull it off.
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Apply masking tape to both sides of where you want your new caulk
bead, with the edges of the tape lining up to exactly where you want
the bead of caulk to stop. This is a technique that professionals use
to ensure a perfectly even-looking bead with no mess. There should be
about an eighth of an inch between the two pieces of tape.
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Anyone know of a guide I could use to make the tape stop? I was
thinking that a yard stick would be about the right thickness. I
could just lay the yardstick on the seam and then apply tape to the
wall/tub.

I know that a wet finger is supposed to go a long way, but last time I
tried I did not like the results. Another problem I had was to keep
the calk coming out in a smooth stream. If I were not so ashamed of
how it looked, I would post my work for a laugh. I just couldn't keep
the tip of the gun in the grove while pumping the gun.