If there aren't any specific statements that are giving you trouble, a pretty broad (and maybe too obvious) suggestion might be to think about in very simple terms what the sentence is trying to say. "Unless" sentences seem to give people trouble, but they make a lot of sense if you think about them in simple terms; "I won't go to the park unless my father lets me"...my father is a horribly controlling jerk who monitors my every move. There's absolutely no way that I can sneak out of the house without him knowing, and he knows me so well that he could detect a lie if I were to tell him that I was going somewhere else. So, if I do go to the park, then my father must have let me. "I'm going to go to the concert unless it rains"...I'm really dead set on going to this concert, and the only thing that could stop me is the stupid weather. Under any other circumstance, I'm going to go to the concert. So, if I don't go to the concert, then it must have rained, since I would have gone otherwise.
If you can remember those, then you can remember how to translate "p unless q" and "~p unless q" sentences, for example.