During use, please make sure that you have taken off the rubber at the tip of the electrode. 

After use, you can clean the electrode with distilled water, and then put on the rubber for storage. Next time when you want to use it, you can firstly dip the electrode's tip into the same solution as the refilling solution. Eg: you can put the Ag/AgCl reference electrode into the 3.5M KCl solution before you use the electrode. 

If you need to store the reference electrode temporarily, you can directly put the electrode into the solution same as the refilling solution. 

The common reference electrodes are:

Ag/AgCl reference electrode &Saturated calomel electrode, which are used in neutral solution

Hg/HgO electrode which is used in alkaline solution 

Hg/Hg2SO4 which is used in acid solution