I've found (with any caulking job) a method that gives nice and repeatable results. First, you put a tape line down either side of the joint with blue painters tape. Next you apply your caulk/silicone to the joint. Smooth the joint using using one of those tools that look like a credit card, or use a plastic kitchen spoon that is wet. If you have nothing else, use a wet finger. Finally, peel off the painters tape while the caulk is still wet.
Your joints still won't be perfect, but the edges of the joints will have nice straight lines and you know before you start how wide the bead will be (because it is the distance between your tape strips).