Place adverb where appropriate?

Hi. I think we can place most (?) adverbs or adverbial phrases, like "also" or "for two years," at the beginning, in the middle or at the end of a sentence depending on what kind of effect (?) you as a write want to produce. (Although for the adverbial phrase "for two years," it looks awkward (if not incorrect) to put it in the middle.) Am I correct?

eg,

Also, he wanted a cup of water.

He also wanted a cup of water.

He wanted a cup of water, also.

For two years, he studied very hard.

He studied very hard for two years.