Another important accessory is the Lens Hood.
ALL SLR lenses have a lens hood to match. So me have a generic type hood, which is basically a ring, some have specially shaped hoods.
The whole point of these is that they block out any light not coming from the same direction as you are aiming, ie. stray light from the side, or just out of the picture.
Some are made of metal, and as such offer extra protection to your lens if dropped or bumped.
Such light causes flair on the surfaces of the glass elements in your lens. This causes bright and low contrast areas/spots which can spoil your images.
A wide angle lens typically needs a wide ring style, like this...
A wide zoom will typically have a more fancy style, flower or crown shape, thus...
Telephoto lenses will have basially the same shape, but depending on the focal length the hood may be deeper or shallower.
This one is for an 85mm lens...
This one for a 100mm Macro...
This for a 50-500 Zoom...
Even if you use a compact or rangefinder style camera, chack your manual, see if it takes a hood!!!
Oh, and these should be used indoors as well as outdoors.
As ever, if you want to know more, just ask.