Caulking a bathtub is very hard! When we caulked our bathtub we used painters tape and left only the part where we wanted to caulk uncovered. We then put a small line of caulk down and smoothed it over with our finger. You can then pull the painters tape off and it will leave you with a nice straight line. Another thing to remember is to fill the bathtub up with water then caulk. Wait untill the caulk dries then empty the water. This is becuase the tub will settle when you have water in it. You don't have to worry about this happening if you never take baths though! Here is a funny video about it!
That video is halarious! Caulking is really messy if you don't do it right! Good tip on the section about using tape to keep the caulk off the places you don't want. Remember to use a lot more caulk around the tub than the shower walls.
