Colorful decorations are the ornaments, garlands, banners and small bright objects that mark a season or a holiday without turning the whole room into a theme park. They do one job: they tell you, walking in from outside, that something is happening right now, this week, this month, and not any other.
The difference between a good set and a disappointing one shows up fast, usually within the first year of storage. Cheap ornaments are hollow plastic with a seam running down the middle, and the paint flakes off that seam before the second Christmas. Better ones are weighted glass or solid wood, hand painted or dipped so the color sits in the material rather than on top of it, with a sturdy metal cap glued in rather than a thin wire hook jammed through a hole that cracks. Garlands are the same story. The good ones have fabric or wire cores that hold a shape when you drape them, so they don't flatten into a sad rope by the second week. If you're starting from nothing, don't buy a huge mixed set. Buy one small box of something in a color you already love, a dozen ornaments, one garland, maybe a string of paper lanterns, and live with it for a season before you add more. You'll learn fast what you actually reach for and what sits in the box unopened, and that tells you more than any list could.
These pieces suit almost any home, but they do different work depending on the room and the light. In a north facing room that gets flat gray daylight most of the day, a warm red or gold piece picks up what little sun there is and makes the whole corner feel awake. In a sunny south facing window, cooler blues and greens hold their own without going washed out by noon. Apartments with small square footage do better with fewer, bolder pieces rather than a scattered handful, because clutter reads as mess fast in a small space, while a house with high ceilings and deep windowsills can carry more without looking busy. Think about the season changing too: what glows under string lights in December can look strange and gaudy under June afternoon sun, so don't be afraid to rotate pieces out rather than leaving everything up year round.
For colors that are easy to live with long term, I'd steer toward one dominant shade with a couple of accent tones rather than a full rainbow in one room, it reads calmer and photographs better in every kind of light, morning or evening. Deep jewel tones age gracefully; neon and pastel together tend to fight each other once the holiday excitement wears off.
Wrap glass and painted pieces individually before storing them, tissue paper works fine, so they don't scratch or chip against each other in the box.