Just because you live in a rental, doesn't mean you have to live with white walls and blah fixtures. But before you start painting or replacing those door handles and ceiling lamps (which is generally allowed), you need to make sure it'll be easy to return everything to the the way you found it ... or risk losing your security deposit.
Apartment Therapy lays out several tips for tracking any changes you make. First off, create a digital list (a spreadsheet perhaps?) of all updates you make, organized by room. Log what you did, the date, the original condition, and where you're storing the existing stuff. If you take photos, record the taking-apart process, as well as before and after shots, the site recommends.
Finally, don't stash the originals just anywhere. Buy a plastic storage container and some bubble wrap so nothing breaks. If you don't have much extra room for storage, consider asking the landlord if they'll hold it until you're ready to put it back.