500 at the beginning, 500 at the end,
5 in the middle is seen,
The first of all letters, the first of all figures
Take up their stations between,
String them all together, and you will see
The name of an ancient king.
500 is D (in Roman numerals), so D___D. Then 5 is V (also Roman numerals) so now we have D_V_D. The first of all letters is A, and the first of all Roman numerals/figures is I. Now we have DAVID!
Finish this saying: "Don't make a mountain out of ..."