There are two good ways to choose the specific style and design of your decorative objects.
Look around at your home
Take in the general aesthetic of your current things. Even if you're just getting started with decorating, it's very likely that you've already collected a few mementos, heirlooms, or other pieces that can dictate the trends you will follow for years to come. Go look at your treasures! What color are they? What metals are they made of? How old are they? Do they have any strong patterns, whether they are small and Baroque or large, bold, and geometric?
Note all of this information down and keep it in mind when you're out shopping. With your mind already focused on what you have, you'll be primed to notice when new items fall in the same pattern.
Look for inspiration in magazines
If you don't have much to go on or if you feel like you'd rather have a completely fresh start, excellent! There's a very fun exercise you can complete to forge your path forward. Clear out an hour or two when you will have no distractions, pour yourself a beverage, and open up a magazine. It doesn't even have to be a home goods catalogue - anything will do. Start to leaf through the magazine. Notice when you come across something you like. Take a marker and circle everything in the magazine that catches your eye. Then, put the magazine down and walk away.
The next day, go in and review the things you circled. Are they of a specific pattern? Do they have similar colors or shapes? Note these details for the next time you go shopping.
If you can't discern a pattern among the decorative objects you've circled, it's very possible that you have an eclectic style, one which delights in diverse and random objects. You'll have to be very careful with how you style these objects, but the result can be very artistic and modern as long as you do it just right!
If it helps, here are some common styles and the types of decorative objects that might go with each style. See if any of these catch your fancy:
Victorian: Porcelain figurines, shiny or scrolled mirror frames, stained glass
Coastal: Starfish and shell figurines, light pastel colors, transparent cylindrical vases, pieces of rope, vials of sand
Rustic or Farmhouse: Baskets, natural wood edges, neutral colors, ladders, distressed frames, decorative plates
Bohemian: Wooden animal figurines, flower art or sculptures, bowls made of natural materials like twigs or leaves, twinkle lights, wall hangings with tassels, tapestries
Industrial: Wrought iron, pipe, bolts, and other 'found' art pieces, blueprints and schematics, dark colors
Minimalistic or Contemporary: Contrasting colors, sleek silhouettes, vases with small openings and cool-toned wooden sculptures
Scandinavian: Bird figurines, geometric wooden sculptures, white frames, star-shaped objects,
Mid-Century Modern: Bold patterns, pops of teal and coral, wooden frames and geometric silhouettes matched to both furniture and decor