Will you share useful life hacks with us?

Never compare your circumstances to those of others because you can always find someone who has it better than you do and this will make you unhappy. Compare your circumstances to your past self.
This way instead of "keeping up with the Jones" you can "improve yourself" which is psychologically far healthier.

Mine are boring but save money. Bicarb of soda and white vinegar are cheap and have a lot of cleaning benefits. Put a tub of bicarb in the microwave to get rid of smells, mix vinegar and water in an old cleaning spray bottle to clean and soak tupperware in bicarb and water.
- Yes! Both so useful...
  I use white vinegar for cleaning the microwave as well - a tub of it heated up fin there for a minute and it makes it much easier to clean.
  And a sprinkle of bicarb in the bottom of a bin to reduce smells.

I don’t live in a warm country, but a 30W fan has more uses than I expected.
During cold weather I can open a window and circulate fresh air very quickly.
It turns out that it dries dishes in the drainer too (it was a fluke that I found that out).
After a shower it can dry the body or get the heavy wet out of long hair while I’m doing something else.

When you go swimming: blow your nose in the shower before entering the pool. That way you won't accidentally have a booger hanging out while swimming.

Dollar bills or candy wrappers are great tire boots to patch a small slash in a bicycle tire.
Most jigsaw blades work in an Xacto #2 knife handle

Wash dishes and utensils while cooking. This way, ar the end, you don’t have a big pile of stuff to clean.
- If applicable: First step of cooking for me is to have an empty dishwasher. Then things go in as I'm done using them.
  
  Yeah, I don’t wash my knives and pans/pots in the dishwasher, only plates, glasses, cutlery. But yes, that could be an option for whoever usually washes everything in there. In that case, the advice is to get everything in the dishwasher the moment you finish using it.

Dropping an alkaline battery on its base is a quick and easy way to tell wether it's full or not. Drained/old ones bounce, fresh full ones wont.
- Another fun battery one - most remote controls work by flashing an infrared LED we can't see with the naked eye, but every cellphone camera can see the flashes as purple light.
  If you think a remote has dead batteries, open your camera app, point the remote at the camera, and push a button while looking at your camera app. You should see flashes. No flashes means the remote isn't working, probably dead batteries.
  There's a lot of Bluetooth remotes out there these days that DONT do this so be aware of that too.
- Also you can deform an alkaline battery to get a little more juice when your remote is dying. Like pinch the sides with pliers.