You have heard the term "location - location - location" in the real estate world, well in tennis, the comparable terminology is "position - position - position."
You might not be playing your best or you might not be feeling your best, but there is no excuse to not be in the best position during the entire point. For doubles, it is especially important to take enough lessons from a qualified pro to always feel comfortable where you are on the court at all times. By being in the correct position you increase your chances of staying in or continuing the point. By being in the correct position you force your opponent to hit lower percentage shots, making more unforced errors.
You cannot believe how many players take lessons and learn beautiful strokes and gain great conditioning, but are highly frustrated by not being in the correct position on the court at the right time. Take some position lessons, they will pay off greatly.
Good luck on the courts!