About the only generalizations I've found that tend to hold true almost without fail that indicate a gal is attracted to you are:
1) She stays or moves close to you without being in a crowded situation in which doing so is inevitable. If there's a lot of space, and she stays close to you, she's attracted. If her breasts or midsection incidentally (or not so incidentally) touch you, she's very attracted.
2) If she smiles at you a real lot, she's attracted.
As for things like crossed arms, they could be signs of shyness or repulsion. Depends upon the person and the situation.