0.2 to 0.3 mm of diametral clearance for something that has to slide smoothly. Push it to 0.4 or 0.5 mm for a lid, a drawer or anything that must never jam.
Unlike a press fit, this is a forgiving target and there is no penalty for being generous. Design towards the loose end.
Why generous is correct here
An FDM part is not smooth. Layer lines on a sliding surface are ridges, and the effective diameter of a printed shaft is set by the peaks of those ridges rather than by the nominal geometry.
A clearance that looks adequate in CAD can be consumed entirely by surface texture, a slightly over-extruded first layer, or the elephant's foot at the base of the part. Half a millimetre of clearance simply removes that whole class of problem.
The sizes that need more
Clearance requirements scale with the length of engagement, not just the diameter. A short bushing tolerates a tight fit; a long telescoping tube binds if there is any misalignment at all, and misalignment is guaranteed on a printed part.
For anything sliding over more than a few tens of millimetres, add clearance and add a chamfer at the entry.
Material changes it
PETG and TPU are stickier against themselves than PLA is, and a sliding pair printed in the same material has a real tendency to grab. Two different materials sliding against each other almost always works better than two of the same.
Nylon is the exception in the useful direction: it is self-lubricating, and a nylon bushing on a printed shaft slides better than any other combination available on a desktop machine.
Print orientation matters more than the number
A hole printed vertically is round. A hole printed horizontally sags at the top and comes out oval, and no clearance figure fixes an oval hole sliding on a round shaft — it binds at two points regardless.
If the fit matters, print both parts with the sliding axis vertical.
The finishing shortcut
A few strokes with a round file or a twist drill turned by hand removes the ridges from a printed bore and converts a marginal fit into a good one in seconds. On any part that will be made once, that is faster than iterating the model.
Work out how much of your clearance budget contraction is eating in the shrinkage calculator. Named fit classes, and which of them an FDM machine can realistically hold, are set out in the tolerances and fit guide.