OK... we can nickname your home a shell, a box, or better: many boxes piled together! Redoing the SURFACES inside will make a HUGE change. When I start any design project, these are the elements my clients and I decide on first - they involve both materials and color (or colors):
Walls Floors Lighting Windows
It might help to have a simple furniture plan to make these decisions, or not! It depends on how detailed you want to be, how many elements will be involved, and how far your budget can stretch, Everyone seems to think that the furniture is the most important part of reworking your "Environment", but once the other elements work together, that's not so. Furniture can be a separate project for later.
If this is DIY: Look for the products, gather samples and then order after you have your colors together, even if you are doing some things later. Paint companies like Sherwin Williams, Benjamin Moore have brochures with colors that work together if you are not confident. They're good!! Use them!!
WALLS: Paint is obviously the easiest product to use (unless it's around your tub, in which case the walls are tile). Paint is also easy to change and you don't need "Standard Off-White" or "Band-Aid Brown" (dorm room color) to be neutral. DO use Eggshell finishes and DON'T use Flat paint (except on ceilings) unless you don't mind repainting all the time.
Can't pick a color? Get tiny sample bottles and paint on poster board as trials.
Make it easy and paint all of the ceilings white. Benjamin Moore 04 is one good color, or any "Ceiling White". If you want drama, paint a color on the ceiling...or even a metallic. If you have painted trim/mouldings, use a shinier finish so it will clean on the doorways. I recommend using half Gloss and half Semi-Gloss (Thank You, Tom Hester) and I also like white trim, but trim to match the walls is OK, if you prefer.
Faux finishes: awesome if you can afford to have real pro do it for you or you can try a kit. It's fun and usually wears better than regular paint. Plus, since it's not a solid color, it hides more, too.
Paper: not that it was ever completely gone, but it's BACK. Textures like grass and burlap or pretend textures or patterns...all available... are wonderful. It's perfect for a Foyer or a Powder Room. Remember: the two rooms everyone sees are your Foyer and your Powder Room. Lots of drama, impact, fun, accessories can be used there. Also, you don't spend much time there, so GO For It!
FLOORS: Re-staining and refinishing wood floors or refinishing stone floors are pretty easy fixes compared to installing either of them new. OR you can use bamboo, cork, stone, tile, and (of course) carpet. Carpet is most likely the least expensive and offers so many options from patterns to a myriad of textures. Buy the best you can afford. I am kinda liking carpet tiles, too. It's "a look" which can be perfect for a home office, basements, etc. Add rugs to your budget if you think they're important, but remember that prices for rugs vary enormously. New blog topic.
LIGHTING: Just changing light fixtures can change the personality of your space. From a center fixture to a track, from white recessed cans to Alzac (a plastic material in clear--which looks silver--or black) or to brushed metals. Light bars in bathrooms to sconces, and on and on. Contemporary taste? Go to Lightology and have a fabulous time! Traditional lighting seems to be sold everywhere, but I LOVE New Metal Crafts where you can buy pretend old or real old and even old fixtures that they will have to wire up for you.
**911: DON'T forget to check on dimming qualities of fluorescent bulbs and fixtures before you change to them!
WINDOWS: This is a vast area in terms of style, color and materials. New blinds (wider -like 1 ½ to 2 ½"), lots of shades will be EASY to find and not too costly. Woven Woods are a new "standard" as are solar shades. Check out the privacy element for bedrooms, baths, and check out the UV elements for sunny rooms or rooms with blues, purples, grays, reds -which fade.
DIY? Try one of the many local retailers in your neighborhood if you don't want to work with a Designer. Paint stores also often carry blinds, also Home stores like Lowe's, etc. They are not always a bargain, though, so check!
Redo any indoor surface element and it can have a big impact. Do more and it will soon look like a brand new place!