This should be easy-peasy to remember:
Farther = distance = imagine the prefix being the word far => FARther
Further = continuance = imagine it is missing the word more as a suffix => furtherMORE
Comment below using both of these persnickerty words in one grammatically correct sentence and I will edit this post featuring your submission.
Further, there will be a gift card involved that would take you farther up the road to Starbucks to spend it.