Choose a container with a wide mouth and fill it with water.
Then go into your winter garden and pick a variety of evergreen stems.
Wear gloves to protect your hands and cut from the back of a shrub or down low near the ground.
If the bush is unruly, it is a good chance to cut off any bits that stick out.
Avoid cutting any branches that will spoil the overall shape of a bush or tree, and don't cut spruce as they do not regenerate if the growing tips are cut off. (You may have nice blue/gray spruce, and that color will beckon to you, but resist the temptation!)
Yews, arborvitae, holly, privet, euonymus, sage, mahonia, pine, cypress, ivy and box are easy to cut and available in many home gardens.
Contrasting shades, texture and form create interest in winter arrangements, so get as many different species as you can find.
Hold the stems in your hand and arrange them so that they look attractive. (Maybe create an outside collar of similar bits.)
Then go inside the house and hold the arrangement in your hand next to the vase so that you can decide on a pleasing height.
Then cut across all of the stems to make them even and the best height for the vase. (For example: one third greenery and two thirds of vase height.)
If using a glass vase, add a few shiny balls to the water before adding the stems.
Once the natural greenery is arranged, add some stems of fake red berries before placing the vase on a red mat.