動機:どうき: usually used when talking about crimes. 'The motive.'

目的:もくてき:$$$: the reason you're doing something - "I'm seeing this movie because I want to have an excuse to say hi to the cute usher."

目標:もくひょう: A goal - usually not something you do all in once. Usually related to self-improvement in some way. "My goal is to learn French in 2 years." "My goal is to run a marathon next July."

狙い:ねらい: ??? not sure how this is different from the others!