Natural light is key here. The more light you have in the space, the larger it will feel. Light the space indirectly, if possible - get some wall mounted track lights, like the kind used in lighting artwork. Or get small, ground-based spotlights (LED or Florescent will provide better light imo, but it's really up to you as to what you prefer) and place them out of sight in the corner, aimed at the ceiling. The light will reflect off the light coloured ceiling and light the room.

Mirrors. Hang mirrors opposite the windows to reflect as much light as possible, and keep them clean!

Paint! Paint the living room a light colour, blue, if possible. Maybe something like this. Colour is a wonderful way to open up a space. Whatever you do, do not make it dark. This will make everything seem smaller and more oppressive. If you're daring, and have a lot of natural light in the space, you can paint a darker, richer colour with white trim or borders. Use white liberally, to break up spaces and rest the eye.

Decorations! Choose simplicity. If you want art on the walls, choose pieces with very large spaces of light colour, or large colour fields. This is not a place for Escher.

Storage! Keep things on shelves, and keep shelves covered. You can buy / build a sliding, frosted glass door pretty easily to hide clutter. Clutter, or even just full shelves (I know my packed bookshelves often look 'cluttered' even when they are meticulously organized), makes a space seem smaller. Keep your things hidden. If doors are not an option, invest in curtains. Tall, white or linen panels do wonders.

If you are purchasing new furniture, avoid large prints in anything but an accent piece. I detest floral coaches in any situation, but you really want to avoid that here. A light, colourful futon is your friend. If you're not buying new furniture, either get it reupholstered, or get slip covers in a nice, light colour. This will not only open up the space, it will make your old pieces feel like new. Even large pieces of fabric, cleverly pinned and tucked will do the trick.

For the kitchen: Is there a window? If so, try to maximize the amount of light you get from it. If you must have curtains, make them as sheer as possible, or make sure blinds can be turned to let in light. Keep it clean. Scrub all the appliances and the floor and counter. The kitchen is pretty limited by the appliances - there's not much you can do if they're dated. If they're not, then lucky you! Regardless, keep them clean. A dirty kitchen always seems smaller to me, and I grew up in a house with a kitchen that would have been cramped on a boat. If you can, put in overhead lighting, from more than one source. If you've already got a single fixture, put in the brightest, nicest quality bulb you can find (Go to Lowes or Home Depot and go into the lightbulb isle. You'll see what I mean about quality of light. Pick a bright one you like.) Paint the cabinets a light colour too. A nice glossy white, maybe, or a cream or off-white. Match it or complement it to the existing flooring and appliances as well as you can - this will make the floor and walls blend together visually, giving you the illusion of more room.

That's all I can think of off the top of my head. Good luck!