Ski with your weight equally distributed on parallel skis.

Literal

Parallel skis [on-に] equally body-weight [object-を] placing ski [polite imperative-なさい].

平行な is 'parallel.' 等しく is 'equally' — the adverbial form of 等しい. 体重をかけて means 'placing body weight on.' The ~なさい imperative marks this as instruction from a ski teacher. A technical sports sentence.