There isn't really any precise definition of what normal would be. One is that the focal length is equal to the diagonal of the frame, but seems rather arbitrary (for 35mm film, i.e. 36mm x 24mm, the diagonal is 43mm).
Another definition I have seen actually makes sense: a normal lens is one that yields prints that have the same perspective as real life when viewed from a normal viewing distance. This is not very precise, however - depending on how large you print and how long your arms are, the normal would be different.
Don't sweat it - just use whatever feels right to you. For me, it's 50mm. For you, it may well be 35mm, or even wider.