Don't wash everything. Always.
Yes. It can't be said shorter.
If you want to take good care of your clothes - and especially the environment - there is no need to wash your clothes very much.
This does not apply to underwear, of course, as it is very close to the body.

A lot of clothes can be freshened up by airing them out. Especially knitwear.
There is actually no need to wash a blazer, a skirt, or jeans very often. These are not clothes that typically get particularly dirty with use. And if there is a stain, you can simply clean the area where the stain is.

It is also a widespread misconception that the best thing you can do is wash something by hand. Hand washing cannot be done without wringing the clothes - and this is where it goes wrong, because in this way the fibers can be damaged - e.g., in wool.
When the label on your new blouse, skirt, or dress says it should be machine washed on a wool program with wool detergent, it's because that's the way to ensure you get the same item out of the machine as you put in.

It is also a misconception that new clothes should be washed before use. Most fabrics are already washed before they are sewn. So unless it explicitly states on the clothing that it should be washed before use, there is no need to do so.

Please note that there may be more than one small label on the side of the clothing.
Read them - your new clothes cannot be exchanged or returned to the store because you have washed them incorrectly.

An important point: There is a big difference between choosing to wash at 30 degrees (gentle wash) and actually choosing a wool program at 30 degrees. The big difference is the spinning. A gentle wash is not the same - and can easily be the reason why your new blouse shrinks a size, as the fibers cannot withstand the higher spinning.

Likewise, it is a good idea to check your laundry detergent. If there are enzymes in the laundry detergent, a single wash can ruin a blouse, dress, or knitwear forever.

Take good care of your clothes - happy airing