Revamp the walls. OK, this isn't surprising advice considering the source, but it still has merit. Lots of manufacturers make repositionable decals with a low-tack adhesive that can be removed without damaging the walls. Hennessy likes stripes, especially for a foyer or hallway.
Create the look of built-ins. Add character by flanking a doorway with two tall bookshelves that reach nearly to the ceiing. Olsen suggests painting them with a bold color such as high-gloss black, burnt orange or emerald.
Replace ugly light fixtures. Most rentals come with cheap ceiling lights and fans. Swap them with pendants or shades that complement your decor, but hang on to the old ones so you can put them back when it's time to move.
Invest wisely. Just because you're renting doesn't mean you have to live with ugly furnishings. Hennessy recommends investing in quality pieces that can easily make the transition to the next place you live, such as neutral upholstery and beautiful bed linens. Rugs can be cut down and curtains shortened or lengthened if they no longer fit your next space.
Bring in light. Position one or more mirrors on a wall opposite a window to reflect the natural light back into the room. You can lean a large mirror against the wall or place a few medium-size mirrors side by side.
Go big with art. No window in a room? Add vibrancy with a large-scale oil painting, even in a small space. Measure the wall and then add a large piece that fits, Olsen advises.