We do all the following:
Don't have a car if you can possibly manage it. We manage perfectly well, even with a large toddler (we are just abandoning the buggy). We walk, mostly, or use public transport. We don't live in London so the buses & trains are about 2 per hour & packed. Live near work if possible.
Not fashionable, but - mend your clothes instead of binning them & buying new ones. When they get a bit scruffy, relegate them to play clothes / extra layers for cold days / painting or gardening etc. I totally use this as justification to buy better quality clothes as they will get worn till they are absolutely past it
Use less detergent if possible. If you're lucky enough to be in an area of soft water supply, you can get away with a lot less detergent in your wash.
Again for the soft water people - use soap, not showergel. It's generally less chemical based, so it's better for the fish etc, requires a less involved manufacturing process, also cheaper & lasts longer if you let it dry after use. I tried oil cleansing too, that may work in hard water areas.
Use a menstrual cup. I love mine. Lasts years & costs way less in total expenditure.
If possible, eat less meat. Grain-fed animals are a pretty resource-intensive way of producing protein. At the very least, try to eat pastured meat.
If possible, try to choose your fresh fruit, veg, meat etc, that has been locally sourced. This has two benefits: it will most likely be in season, so will probably have required less resources to produce it, as opposed to something grown in a heated greenhouse. Secondly, lower airmiles. You also get the benefits of knowing that it's likely to be fresher & more nutritious, as many many foods start to lose their nutritional value once they are harvested.
Turn all lights, appliances etc off if you're not using them. Never leave on standby.
Plan your meals for the week. Don't throw food away because you failed to plan to eat it before it expired.
Don't use a tumble dryer if possible. It's possible to manage without one, as long as you have a bit of outside space for drying. We use 2 clothes horses & a line, put it outside, then bring in at night or if it looks like rain. Even in winter, as long as it's above freezing point.
Wear a jumper or put a blanket on the bed if you're a bit cold. Interesting how in the first world, when we're cold, most people's initial response is to alter their immediate environment. The more sensible response is surely to insulate more - yourself, and your house.
We avoid palm oil if possible, and any products with it in unless they state that it's sustainably produced.