Sign up for a health savings account and USE IT. (United States specific advice.)

It lowers your taxable income. The only caveat is you have to remember to use that money to buy things you were already going to buy anyway. Convenient hack to know what you can and can't use: Doordash now labels HSA-eligible items at CVS. You don't have to actually use Doordash to see which items you can buy with your HSA card.

Pretty much every item of clothing I own is from the thrift store or has been second handed in some way. I love being able to find clothes that are more my style without the $70+ price tags and I'm able to maintain a business casual wardrobe required for my office.

Furniture that isn't beds are all second hand as well, I just steam clean everything upholstered. Buying brand new is a money making sham that only fills our landfills unnecessarily.

Also, learning how to cook has saved us a lot of money of takeout and prepackaged meals. There are so many ways to learn now too.

We also no longer own a vehicle, we walk, bike, or transit everywhere. I do maintain a license so I can rent a car when necessary though. Vehicles nickle and dime you to death when you own the outright or cost a years wages or so to buy, plus gas and insurance prices are insane. It costs me $500 a year to ride the bus.

https://freecycle.org

A hot water bottle to stay warm in winter. Also a really good tip if you're not poor.

steal

Buy a 6 pack of good wool balls. Finish up using your fabric softener first and never buy any again.

Never buy plastic/paper/whatever bags in supermarkets. Bring yours and if you forgot them for whatever reason, lurk for trailing cardboard boxes. Supermarket are often filled with those. They are solids and the supermarket is going to thrash so they don't care.

Same when you move out, don't buy boxes. Go to your local library to ask them to put aside some cardboard boxes for you. Books cardboard boxes are really solid and always clean. When you are there you can also buy Mutual Aid: A Factor of Evolution by Kropotkin.

Make a youtube compilation channel and profit off of other people's content.

Go to Germany to get groceries cheaper and VAT free.

If you do have debts - try to consolidate them wherever possible. Don't have more than one credit card adjacent means of payment (store credit cards or similar).

If you find yourself with extra money, try to pay off debts first, or at least make extra payments. Reducing debt repayments over the forward term can have a huge effect.

Decide how much you will spend each week and spend a little less than that, slowly over 3 months you will reduce your expenses. Buy clothes and wash them after 2-3 uses unless you live in super dirty/dusty/warm area. This will prolong clothes life significantly and added advantage is they come back in fashion after a while. I have a shorts which I use still after 10 years.