Without a car, use a bike to get around (I'm doing this for +20 years now, despite everybody says its not possible. IF you urgently need a car, for example you have to move something big and heavy: just rent a car/van/whatever. Done)
The second most effective thing: Probably let go of all your plans about flying via plane.
Beside that, in your household, using HOT WATER accounts for 10 up to 30% of your annual energy bill.
I "found" out, that using about 36 to 38 degree Celsius warm showering water is most ideal for your skin (and no, it does not feel cold! It feels warm, not hot, not Luke warm, just warm as in very comforting). So if you use just warm water for showering, you might decrease your overall boiler temperature, which mostly is set above 60 C.
Beside ALL this: Spread the word and show everybody that changing is not hard at all and it even is promising a longer life (due to more biking, less products to "repair" your dried out skin due to too hot water etc.)
E.g. when grocery shopping: Bring your own reuseable bags. Stop putting vegetable/fruit in a plastic bag each. You're gonna wash them anyway. Avoid buying veggies, fruit, sweets, whatever that's first wrapped in single/small units of plastic packets, then put on a plastic tray, and finally wrapped again in a bigger plastic bag.
Pro tip: for seasonal produce and stuff that grows locally, buy at your local farmer's market if you have one, supporting your local small businesses/farmers while you do it. Win/win because you'll also reduce the environmental cost of shipping produce across the contintent to you.
When shopping for clothes, don't buy five $5 t-shirts that fall apart after 2 months. Buy one $25 t-shirt and wear it a little longer. If more people did that, producing millions of ultra-low-cost clothing items in Bangladesh for cheap and shipping them halfway around the world to you on a huge container ship - arguably one of the biggest and worst causes of pollution in the world - would stop being so profitable.
When shopping for cars, go electric, but only if your power company offers a plan for electricity from renewable resources. Research if it's really produced that way or if the power company is only buying CO2 certificates for the money while still giving you good old coal power.
If you only need to go a few blocks away, don't take the car. Get a bike, a scooter, a skateboard, or just walk. Win/win for your health and fitness, too.
If you have a garden, don't mow the lawn each week. Let it grow a little wild if you can. At least allow some wild flowers or whatever to grow. You'll give bees and other insects a home, and you'll help offset at least some of the damage we've been causing in that area. A neatly trimmed lawn bears very little life.
I don't have time for more right now, but this is basically what comes to mind whenever people ask me what they can do, or why they should do something. Every little bit helps, will inspire others, will stack, will multiply, will grow. Lead by example and more will follow. Vote with your wallet and as more and more people do it, the profit margins will shift.
The defeatist attitude of "how can it even matter what I do when I'm only a millionth of a percentile of the cause" is idiotic. Do you expect others to do it if you won't even try?
I would suggest becoming Amish.
