Not resetting the camera
It’s a good idea to develop (and use) a default ‘grab and go’ set-up that the camera can be reset to once you’ve finished taking a series of pictures. Doing this ensures that you can change any settings from a familiar set of parameters. For instance, if you forget to reset any exposure compensation you’ve dialled in, then subsequently dial in some additional compensation, you may end up with horribly over- or under-exposed results. The same can happen if you haven’t switched the camera to your preferred shooting mode or metering pattern, or if you’ve left the ISO really high.