If you've got any outside space at all, a balcony, a patio, a strip of yard, this is worth taking seriously. If you're dealing with a shared courtyard where everything grows legs and wanders off, maybe keep the good stuff indoors and furnish the outside cheap.
Color is where most people overthink it. Anything bright gets tired by the second summer, and that includes the orange planter I was so pleased with that now just looks like a traffic cone full of dead basil. Go with weathered wood tones, charcoal, muted greens, the kind of gray that already looks like it's been rained on. Those colors forgive fading instead of announcing it. Metal finishes are the same story: a powder coated black frame ages fine, a cheap bronze paint job starts flaking at the edges within a year and you end up with something that looks diseased rather than distressed. Natural materials, teak, stone, galvanized steel, don't really have a wrong color because they're not trying to be a color, they're just trying to survive outside, which is the actual job.
The bigger split is between things built to live outdoors and things just put outside and hoped for. Real hardwood furniture, proper stainless or galvanized hardware, UV stable fabric, will go silver gray and look better for it, the way a deck does. A pine side table from a bargain bin will warp, the joints will open up, and the fixings will rust streaks straight down the leg within a season because someone used regular steel screws instead of stainless. Cushions are the worst offender for this, the foam inside a cheap one holds water like a sponge and grows something you don't want to identify, while a proper outdoor foam drains and dries in an afternoon. Maintenance is mostly just not skipping it: wipe things down, bring cushions in when you're not using them, oil hardwood once or twice a year if you want it to stay honey colored instead of going gray, and check that any metal legs sitting directly on stone have some kind of pad or they'll streak the patio by June.
When you're buying in store or the day it arrives, turn it over. Check the legs are actually attached with proper hardware, not glue and optimism, check drainage holes on planters are real holes and not decorative dents, and check any fabric zips and seams before cushions get rained on once and never dry properly again.
The good ones have a weight to them when you pick them up, and a drain hole exactly where water would actually collect, not just somewhere convenient to drill.