You may already know this, but you can set the shutter speed and aperture independently - pull back on both sides of the black shutter speed ring to turn it, or pull back on the left side and use your other hand to change aperture (the aperture control ring has one tiny serrated patch under the lens).
And make double sure you've locked the film door properly when you close it. If you leave the door release in the open position, the door will still close on the catch - but then pop open when you put the camera down. Go on, ask me how I know.
