A "motivated" person not only works hard, but is also proactive, which means that they look for things that need to be done without being asked. People can be "motivated" to do work, or to do other difficult things like sticking to a diet:
The key to successfully accomplishing one goal after another is staying motivated.
The most common adjective used together with "motivated" is "highly". It means "very", but "highly motivated" sounds a lot more natural than "very motivated". Some other adjectives that go well with "highly" are: