The inexpensive route - remove the landscaping from the sides, about 3' on either side to open it up and just put mulch with clean edge. Put a large urn on either side of the door where the landscape was to create instant architecture and a sense of a threshold. Paint the door a bright color, maybe white or yellow, and frame the door with a light fixture on either side, or if you can't do that because it is a rental or something, maybe you can use some solar lights. Something to add architectural elements. If you are able, you could extend the trim with another layer to make it wider and more prominent. Making the house number prominent is also a good idea, you could use something decorative like a small sign or a pretty wall plaque. Maybe a welcom mat :)