In the past 6 years we have lived in seven houses, by now I like to think I have a few tricks up my sleeve about brightening up a rental property (low cost). We just (last week) not only moved houses, but cities and where most people find moving stressful, I actually find it quite fun. Playing with new interiors, learning how your furniture will flow thru a house, what spaces are most usable at what times of day depending on the light, the noise etc....
Plants are a great inexpensive way to introduce color and beauty into a home. We went to our local mitre10 and picked up (off the discount table) a few plants and some soil, I already had a collection of pots.
One thing to remember when re potting new plants, often plants from a garden centre are root bound meaning when you take them out of the pot the roots are woven together tightly, easy enough to solve, just soak the plant roots in some water to loosen them up.