It's amazing what a coat of paint can do on kitchen cabinets. If you do them a light colour the room will be transformed. A pale sage green, or a rich cream, perhaps?
Elsewhere, I agree about lamps making a big difference. You can get rechargeable ones (try Pooky.com) which means that you aren't restricted by the position of sockets. They even do wall lights that don't need an electrician to fit, and you can put table lamps on shelves or mantels without having cords trailing and looking messy. Just be sure that all the bulbs are the same colour - having a mix of 'warm' and 'cool' light can look wrong.
If redecorating a whole room is out of the question, look at touching up any chips or scuff marks on paintwork, as they can make a place look neglected. You can buy little bottles of gloss paint that are designed for touch-ups. They are like liquid Tipp-ex, with a tiny brush in the lid.
Every now and then I do a refresh by moving things like pictures and ornaments from room to room, just ringing the changes. Even changing the position of plants can make a difference, as you are looking at something 'new'. Far less drastic than decorating, but it helps. I think it's known as shopping your own home, and it means you don't end up with far too many 'things' when you fancy a change.
There are videos on YouTube about interior design that might give you ideas, too.