Tell the truth.
Make sure you are honest about your intentions. Being dishonest by saying you are looking for a friend is how guys end up the friend-zone or quickly rejected. You do not have to be blunt, however. You can use euphemisms. For example, instead of saying, “I’m looking to hook-up and then never speak again,” you could say, “You are a really fun person, and that’s exactly what I need right now – someone to just have a good, casual time with.” By being clear, you are not misleading her and you’ve taken control by setting the tone.