There really is only one question when it comes to decorating a rental: "What will my landlord let me get away with?"
This is our 3rd week living in our rental home. Already the transformation has been incredible. I'll share with you a couple of simple things we have done to change transform our rental from shabby to chic. You may or may not be able to implement all of these ideas but hopefully you may be able to use some of it.
1) Befriend your landlord!
OK, so you don't need to become BFF with your landlord but it sure helps if, in those few minutes/hours that you have contact with your landlord, you become friends or are at least friendly to each other. This is easier with a rental home where you are renting directly from an owner (not a property management company) than in an apartment complex. Apartment managers don't own the property and have certain rules they have to follow.
Chat it up with your landlord every time you have contact with them and hint at changes improvements you would like to have them do or do yourself. A lot of the time they will agree to let you change something (paint, light fixtures, etc.) if you do it yourself and often will deduct it from the rent dollar for dollar (keep your receipts.)
That being said, be honest with your land lord. Don't tell them that you are a master plumber and want to change out the bathroom sink when you haven't the slightest clue about plumbing. It will come back to bite you in the rear and will harm the relationship with your landlord and could possibly lead to eviction (if you really mess up and damage the house.)
2) Clean your windows.
...And let the light in! Nothing spruces up a room like sparkly clean windows and unobstructed views of the outside. I like to use whatever window cleaner I have lying around, or you could use a vinegar/water combo, and a nice large pile of black and white newspapers. Yes Newspapers! The bums really do know what they're doing!
I've been cleaning my windows like this for years and you will get crystal clear streak free windows this way! Just spritz your cleaning solution and then wipe down with a crumpled up sheet of newspaper. Trust me it works.
You could do the same thing for the outside of the windows, that is if you can reach them all. Usually I use outdoor Windex that attaches to your regular garden hose. It works ok as directed but for the windows I can reach I like to scrub them down with one of those sponge mops before rinsing.