The best place to work with the element is outdoors where you can feel and see them around you. However, if you are unable to make it outdoors you can still bring the elements to you. Use representations of those elements on your alter. Bellow are some examples of what you can use.
Air: Direction- East Colour-yellow
feathers, fans, dream catchers, wind chimes, incest
Fire- Direction-south Colour-red
candle, lighter, burnt charcoal
Water- Direction-west Colour-blue
cups, sea shells, sea weed, water plants
Earth- Direction-North Colour-Green
rocks, pebbles, sticks, soil, root vegetables