What is the procedure of designing a salt bridge for a galvanic cell? I'm doing an experiment where I'm measuring the effect of changing the $\ce{Cu^{2+}}$ ion concentration on the voltage in a copper-zinc galvanic cell. 

I'll be doing at least five trials for each of the five concentrations I'm testing for (from $0.2-1.0\:\mathrm{M}$), so in total that is 25 trials. However, do I need a new piece of filter paper as a salt bridge for each trial, or can I reuse the same piece of filter paper and dip it in a $\ce{KCl}$ solution each time? Do I really need to make 25 separate pieces of filter paper?
If you wish to do 25 trials with 5 trials per concentration, I would suggest the following:


You can use the same filter paper as long as the $\ce{Cu^{2+}}$ concentration remains constant. However, since you are changing the concentration 5 times, you will need 5 pieces of filter paper.
After every trial, thoroughly wash the filter paper with distilled water. 


So I would say you need at least 5 pieces, but you would not need to go all the way to 25 pieces. Just make sure to follow step 2 after each trial.