Mars is weak when in its fall (Cancer), when aspected by malefic (like Saturn and Rahu), when combust, and when in difficult houses for it (the fifth, eight, ninth and twelfth).

Mars is generally a benefic planet for Cancer, Leo, Sagittarius, and Pisces ascendants, and is usually good for Aries and Scorpio as well. Here its positive qualities like energy and insight can be improved, even if it is not weak.