Some of the tricks I've learned are to use light colors, mirrors to reflect light and make spaces look larger, and good lighting. Glass top coffee and end tables visually expand your floor space. Upholstered pieces with legs also visually expand floor area. Big, dark pieces that sit right on the floor take up space and make your rooms look smaller. Go for sofas with clean lines and classic styling. No big huge rolled arms or overstuffed cushions, etc.
BTW, Ikea has some good furniture for small spaces.
As for art, I've found that a few large pieces make more of a statement than a bunch of small pieces scattered around. Pare down accessories to "just enough" - don't overdo, or you will end up with a cluttered look. Go for a few good looking pieces rather than dozens of little tiny stuff.
Keep clutter to a minimum, and keep your place clean and picked up as much as possible. This will help so much.
Opt for double duty pieces such as night stands or end tables with drawers, storage ottomans, chests and trunks, etc. Armoires keep televisions and elecronic equipment out of sight.
Keep windows sparkling clean, inside and out, and use lightweight or sheer fabrics for window treatments. Stay away from fancy swags and layers and "funeral parlor" looks. Keep it simple to let it natural light and give a feeling of airiness.
P. S. - I am having my carpet ripped out and laminate flooring installed throughout. I've got everything packed away and pared down to the bare minimum, and I like the look so much I'm thinking of doing some editing when I put things back in place. My little Barbie doll place looks so much more open and spacious.