Avoiding mold formation

The most important tips to prevent mold formation.

Construction measures

Let newly constructed buildings dry long enough.
Equip bathrooms with suitable windows or a ventilating fan. Make sure to always air the room after showering. When using a ventilating fan, make sure it runs for another few minutes after being turned off (e. g. in case it's linked to the light switch).
Let the walls breathe: Avoid paint or wallpapers that seal off the walls airtight.
Fume cupboard: Every time you're cooking, a lot of water evaporates and has to go somewhere. Make sure it goes outside, or it will condensate on the walls and provide good living conditions for mildew.

When having mold infestation behind furniture like cupboards or couches, try leaving some space to the wall to allow air circulation.
Avoid airtight curtains or curtains which heabily obstruct air circulation. Especially near niches and corners.
Consider using a dehumidifier. Obviously, if you have been using humidifiers, stop it. You can use a hygrometer to measure air humidity and check if it's too high. Ideally, it stays below 55%.

Air the room consistently and correctly: shock-ventilate for several minutes several times a day. With wide open windows and doors, so the air can be exchanged quickly and thoroughly.
Heat rooms even if they are rarely used. Just because you don't use it often doesn't mean you should let it cool out. Make sure the surface temperature of the walls is sufficient by heating all rooms at least somewhat.
Regularly emptying the bin: Don't give your trash the opportunity to evaporate humidity and spread mold spores.
Don't leave wet clothes like jackets, ski suits or shoes in curtains or niches. Make sure they can dry swiftly.
If you are air drying your clothes, don't do it in your apartment but outside or in the basement or in the attic. Or consider getting a laundry dryer.
If you're using a laundry dryer, make sure the exhaust air goes outside rather than inside the room.
Regularly check your living space for mildew to make sure you can react early to a possible mold problem.