What is the best fixation for fluorescence microscopy of GFP tagged proteins?

For fluorescence microscopy of GFP tagged proteins, the best method for fixation is to use fresh 4% PFA (paraformaldehyde) in PBS, buffered to 7.4 pH. The cells should be fixed for 15-30 min in room temperature and then washed well with PBS before moving on to blocking and permeabilization.