1) Don't delete photos on your camera. Delete on your computer instead. Why ? Because there's a theory that deleting in camera can cause the card to error and fail....photographer's worst nightmare
2) To blow dust off your lens with your mouth, hold it in the air so your spit doesn't make matters worse
3) Learn how to be a human tripod. For those times you need a slow shutter speed and you haven't got a tripod. Spread you feet apart, so you're standing on a firm base. Hold your elbows into your body to prevent your arms and hands wobbling about. Hold your breath when you take the shot, to minimise any movement. With this technique, you might be able to hand hold a 1/4 sec' exposure
4) If you have a camera with interchangeable lenses, point your camera down when you change, to minimise the amount of dust entering the camera
5) For portraits, use a white board or sheet to reflect light into the subjects face. These are called 'reflectors'
6) Always carry a spare battery