This is a HUGE topic, so let's just start! I can put furnishings styles into several categories, but they merge to Modern, Traditional, "Eclectic" -- or a controlled combination of styles and "Transitional" -- not modern, but not fussy). There's also Asian, Primitive, Country and various specialized styles of serious antiques. There is also very customized (what I call) "Art Furniture". All styles are Always available Somewhere. Serious antiques aficionados won't change their taste too much and will always find what they need. Many young people like cleaner lines, usually more contemporary or modern -- which also can include all kinds of classic modern furniture from mid-20th Century. Assuming that you are not, at least for now, working with a Design professional, what do you "do"? Follow your instincts. No matter how old you are, this is YOUR place, not your mother's. It's amazing how often I hear someone say that they are tired of living in the style of their parents or in-laws, and that's not just "20-somethings".
And look around you! When you're looking, unless you know that you are of the temperament to replace what you are buying SOON (and that means in less than 10 years), give your purchases some thought. In furniture, trends tend to follow and coordinate with structural designs: houses in the 50's, 80's and the past 10 years have colors and scale and styles of furniture that are different from each other and the latest trends. I totally remember looking for purple upholstery fabrics in a year when I only found 3 (three) samples after perusing about 5 textile showrooms at the Mart. And now would be lots easier. Or, when trying to replace my own sofa fabric, I couldn't even find a supplier to custom dye the color I was seeking. Then, just 3 years later I started to see the color "everywhere"-- sort of.
If you are shopping retail, which is a where most of us start, pay attention to what is "AROUND" now in contrast to what you find from time to time, as well as what you may really love and think it doesn't exist. You can perhaps look on line and/or go in person to some wonderful, more specialized dealers like Design Within Reach & Pauline Grace, Orange Skin -- for classic modern/contemporary, Golden Triangle & Primitive --Asian and primitive). They might have something that wonderful, stylish look that is not what everyone else has. Thrift and resale shops will carry everything from something recently acquired and quickly unloaded to something that was perhaps just hanging out in the same room for so long that the owner just wanted a new color. Some of the best products (Baker, Widdicomb, Directional) can be found at such reasonable prices and if you like the style, reupholstering or refinishing is most likely well worth the cost.
Even more important than "portable furnishings" be sure to give thought to anything permanent you install/build-in: cabinets, tile, lighting, stair railings. If you haven't seen homes that inspire you, books on various styles might help. To this list add crown moldings, door hardware, counter tops, faucets, plus almost anything that a contractor or any of his/her subs would install. These are the permanent and semi-permanent (as I call them) decisions that will designate your house as modern, traditional, neither or trendy (which is short-term). Over my years of working in Design, I have seen the ebb and flow of Harvest Gold, Copper Brown and Avocado (and in my childhood Pink and Aqua) appliances. (Yep, pink is somewhat available again.) Who knows if the stainless steel "look" will be as popular in a few years? It was once only considered modern.
I've also seen bizarre lighting, shiny chrome, shiny brass and bronze doorknobs (although those ALL somehow still squeak through) and all materials and colors of kitchen/bath/bar cabinets (plain white to highly carved dark brown). Of course, some of those items are (supposedly) "back". Wallpaper is in style again, too, but probably not the same colors and patterns from the mauve and gray 80's.
If you can find your way to your own style, it's fun and wonderful and gives you something to watch for in furnishings, plus (my favorite part): accessories and art. Modifying and adding to the "bigger pieces" will be fun and ongoing. Each paint company has hundreds (probably thousands) of colors, and that's for YOU to choose from and work with. Off-white is NOT your only choice (unless you have to repaint it for a landlord in a year)! If you are finding that you are choosing that same sofa that your neighbor has, maybe in almost the same color, it will probably look out-of style and out-of-touch even before it wears out. It will be "out" even faster if you can buy it from several different places, because then you KNOW it's trendy. For the past months, I have observed the McMansion decor of the past decade retreat and a bit more individuality and variety show up in the marketplace.
Is there anything wrong with "safe" and "neutral" as your look? No! It's an easy backdrop for the art and accessories I love to see complete a space. And realtors love those neutrals for "Staging" if you plan to move soon. But don't be afraid to break out and try something (reasonably) adventuresome, especially if you can take it with you when you move, or work around it if you re-do.
DESIGN SENSE: What you have or need to choose or make something attractive and comfy. Is it "in you" or can you find it?