i have a few grammar questions:
what is the difference between 하게 and 히?  for example, i said to my friend 조심하게 운전하세요 and she corrected me and said it should be 조심히.  what is the difference in these two conjugations?  
also, i haven't found any set rule for conjugating to the 이/히 form of any verb/adjective.  and the examples i've found don't seem to follow a pattern (조용히, 다행히, 많이, 깨끗이).  is there a rule or pattern for this?  
i am also looking for a rule about using ㅁ/음 to change a verb to a noun.  again, the examples i've found don't seem to follow a pattern (도음, 죽음, 삶).
and my last question is about adding ㅅ in cases like 어젯밤.  could someone please explain why the ㅅ is added and exactly when it should be added?  i think this has something to do with putting two nouns together?
thanks for any help!