There's some overlap between them and the nuances are difficult, but I think some major differences can be summarized as:
목적 is often the objective or purpose of something. It is thus often used in form X의 목적, meaning the purpose of X:
인생의 목적 (the purpose of life)
안전의 목적으로 ... (for the purpose of safety)
이 연구의 목적은 ... (The purpose of this study is ...)
목표 is a goal or target. If you're talking about sales goals, that's a target, so it's better to use 목표. If you're talking about your goals in general (not for a specific purpose) then it's better to use 목표.
내년의 목표는 ... ([My] goals for next year are ...)
However, I believe there will be a lot of overlap in these cases, and 목적 may be acceptable when talking about "objectives" in general.