oregano, parsley and basil

I am really worried about my herbs.  i worry they aren't getting enough sun, are too wet, not wet enough, don't have good enough drainage.  they keep looking the same or worse.  basil with shriveling leaves near the top.  i think im supposed to pick near the top.  oregano is pick on the outside near the bottom and parsley is near the bottom i think.  i wish i would have only bought one herb at a time.  i keep reading stuff online but i get more confused.  ....... boo......