Heat is the one real enemy
PLA starts to soften at around 55–60 °C. A room never gets that hot, but a parked car in an Indian summer, a sunny windowsill behind glass or the top of a warm appliance can.
A softened print can sag or warp and will not spring back. Keep prints out of cars and direct afternoon sun, and they will hold their shape indefinitely.
Cleaning
Dust with a soft, dry brush; a clean make-up or paint brush gets between the segments of a flexi toy. For marks, wipe with a cloth dampened with cool water and a drop of mild soap, then dry it.
Do not use hot water, a dishwasher, or solvents such as acetone and nail polish remover. Hot water can warp the print and solvents can dull or damage the surface.
Handling flexi joints
Joints are designed to swing in one direction. Bend a flexi the way it naturally moves. Twisting a segment sideways or pulling two segments apart is how links break.
If a joint feels stiff when the print is new, work it gently back and forth a few times.
Planters and anything that holds water
3D printed walls are built from layers, so a planter may slowly seep if soil is kept wet against it. Keep the plant in its nursery pot and use the printed planter as the outer cover, or water sparingly as you would for a succulent.
Colour over time
Indoors, colours stay true for years. Months of direct sunlight will eventually fade most filaments, especially bright ones, which is one more reason to keep prints off the windowsill.