Bet you didn't know that you had rules to live by when it comes to decorating your apartment, but Apartment Therapy begs to differ with their "10 Commandments".
First of all you should definitely decorate, even if you won't be there for long and even if it's in small, easily removed ways. Otherwise, your space will never feel like home and you can feel depressed every time you open the door.
Spend your money on items that have a lot of versatility, so you can use them in your next apartment, whatever that may look like. A couch that can switch from left to right handed, tables that have additional leaves or double as storage are all great choices.
Lighting is often horrible in rentals, especially older ones, don't feel like you're stuck with what's there. Even if you can't swap out the overhead lights, you can fill your space with lots of great floor and table lamps.
Replace the hardware on the drawers and cabinets in the bathroom and kitchen for a complete make-over. Just keep the original knobs and pulls in a safe place and put them back when you move out.
Window coverings are usually abysmal in rentals. So make sure to cover what's there with new curtains (IKEA is a great place to find cheap ones) or roller blinds.
If you can paint, go for it, but if you can't, use temporary measures, like removable wallpaper or wall decals, to make a big (non-permanent) impression.
Rugs can cover an ugly floor, a stained carpet, and just generally bring color and pattern to whatever room they reside in. Invest in area rugs you love because you can take them with you wherever you go.
Display art, even if you can't hang it on the walls, by leaning it against walls or using removable 3M strips to attach it to the walls. From print it at home sayings to original works, there's something for every budget and every taste out there.
Finally, focus on the great stuff about renting, like you can spend your money on new furniture rather than emergency repairs. If something breaks in your rental, you can call maintenance and get it fixed for free.