Plant a row of shrubs along the ground in front of the porch. This can provide a visual barrier if there is no latticework or other covering over the gap between the porch and the ground.
Plant flower beds on the ground in front of the porch if you do have latticework. This allows the latticework to be seen while providing color to the front of the porch and breaking up the monotony of the straight lines of the porch. You could also use an alternating pattern of shrubs and flowers.
Place flower boxes on the railing along the edges of the porch.
Install hanging baskets from the roof along the edges of the porch. Using plants that produce long, flowering vines can provide splashes of color while also providing some privacy by blocking the view of others.
Install landscape lighting. This can involve any combination of rope lights wrapped around the posts and railings, installing track lighting in the beds in front of the porch, using track lighting along the walk leading up to the porch, or installing spotlights to highlight the porch.