There are 3 essential pieces of kit you should not be without, 2 filters and one Tripod.
On this page I will talk about Filters.
The first filter you should get for each of your lenses is a Skylight or UV Filter. This screws onto the front of the lens and affords protection to the front element of the lens from knocks, scratches and dust.
If the front lens element of any lens gets damaged or scratched, the lens will not provide the quality the manufacturer intended. This Skylight or UV filter should stay on the lens at all times, except when you fit a Polarising Filter (see below). The skylight or UV filter looks like clear glass, and the diameter to purchase can be normally found stamped on the inside of the lens cap in millimetres, e.g. “52mm”. Bring your camera along to your photographic supplier and they will supply you with the appropriate sized filter. Alternatively you can order online from the various suppliers.
The second filter you should seriously consider is a Polarising Filter, which fits to the front of the lens, like the Skylight or UV Filter. It consists of 2 sheets of polarised glass which rotate against each other and is dark in appearance, and will result in reducing the amount of light entering your camera, which means longer exposures. Why on earth would you want this?
Well, Polarising filters, like Polarised sun Glasses, drastically reduce, or cut out entirely, reflections from water or shiny surfaces (like some leaves), shop windows and so on. They can also dramatically deepen colour saturation, especially in clouds and blue skies. They can remove the reflective sheen from the surface of water - we've all seen pictures of boats apparently floating in the air. They work best when at 90 degrees to the direction the camera lens is pointing.
For digital cameras, make sure you get Circular (not Linear) Polarising filters.
Have a look at the Wipikedia explanation which gives good before and after pictures for comparison - here's the link - https://en.wikipedia.org/wiki/Polarizing_filter_(photography)
As the quality of the filters directly affects the way your camera “sees” the images, do not skimp and buy the cheapest filters you can get. Reputable makes are Hoya, Lee, Tiffin and Cokin to name but a few. See Links page for websites.