The thing nobody tells you about small decorations is that they are the first ones to get lost and the last ones you'll miss. A big tree topper gets put away with care every January. A two inch glass bird rolls under the sofa and stays there until July. Buy more than you think you need, and keep them together in one box, not scattered across three different bins, or you'll be down to half a set by the third Christmas.
If you're starting from nothing, go for a set of plain glass or wood ornaments in one size before anything shaped or themed. Small decorations read as clutter fast when they're all different heights and stories, so a consistent size gives a tree or a mantel some order even when the shapes vary. These are the pieces that fill gaps between the larger ornaments and the lights, the ones that make a tree look full rather than sparse. Where they stop working is when a room is already busy, a patterned rug, a gallery wall, a mantel crowded with photos and candles. Small decorations need a bit of plain space around them to actually be seen, otherwise they just disappear into the noise and you've spent money on decoration nobody notices until they're packing it away. On a small side table or a narrow shelf, three or four is plenty. Beyond that it starts to look like you emptied a drawer.
Color is where most people overdo it. I went through a phase of buying every small gold ornament I saw because gold photographs well, and ended up with a tree that looked like it belonged in a hotel lobby, not a living room. What's easiest to live with, year after year, is picking one finish and sticking close to it, so matte white, or warm wood tones, or a muted red, rather than four competing metallics fighting for attention on the same branch. Mixed finishes can work but they take more restraint than most of us have standing in an aisle in November. A few matte pieces mixed with one shiny finish looks intentional. Five different shiny finishes looks like you grabbed whatever was left.
This kind of decoration suits a home where the big pieces, the tree, the lights, the stockings, are already settled, and you're just filling in the small spaces that make the whole thing feel finished rather than half done.