It is a little tricky to tune your guitar to Drop A. The standard guitar strings will probably not hold up to this tuning as it makes strings pretty loose and buzzy. Upgrading to thicker gauge strings (0.012-0.056) can solve this issue. Once you have the right strings, all you got to do is tune down every string other than the Low E to the perfect fourth from the standard tuning. That way, A D G B E becomes E A D F# B. The Low E tuned a further whole step down, making it A.