How to use 'hardly' correctly

Many students make sentences such as the following with ‘hardly’:
a) He works hardly because he wants to obtain good results in exams.
b) The man beat his enemy hardly so that he would run away.

Actually, the above sentences are wrong and should be replaced with:
a) He works hard because he wants to obtain good results in exams.
b) The man beat his enemy hard so that he would run away.

‘Hardly’ is usually used in the negative sense. Look at the following sentences and their meanings and you will understand how to use ‘hardly’ correctly.
a) She could hardly wait to see the present from her aunt.
[‘could hardly wait’ means ‘could not wait’]
b) He hardly came here to help me with this work.
[‘hardly came’ means ‘did not come at all’]