Firstly, use the factor theorem to determine one factor. Substitute factors of 24 into the equation, beginning at plus or minus 1 and then increasing. The first factor found will be -2, therefore (x+2) is a factor.
Using polynomial division, we find that (x3 + x2 -14x-24)/(x+2) = x2 - x -12. This can be easily factorised into (x-4)(x+3), so the final answer is (x-4)(x+3)(x+2).
This can be checked by expanding the brackets.