"Take only what you need." It is a sad truth that humanity cannot function in modern society taking this fully to its literal meaning. If one were to try to only use a few trees on their land to build a small home that could shelter them from the weather, you'd be thrown out for nor paying your taxes. Rather, what I mean by this phrase is that we should do our best not to waste.
A lot of energy went into growing that tree from seed to spruce, simply throwing what you didn't use to build with would be a disservice to all the time, the decayed animals whose bodies fertilized the soil, the animals that made that tree their home, and too numerous other relationships to mention. So, when chopping down that tree for firewood, don't throw out all those splinters, use them for kindling, use small branches to carve out jewelry or cookware, the options are near limitless.
The same goes for animals. I may not have much use for deer entrails, but plenty of animals do. If I am using my own land to hunt them, I'll field dress the animal before taking it home to butcher for meat, allowing the wolves and other predators that would have normally been the ones to eat that animal some recompense for taking their meal from them. Starving another to feed myself is inhuman. Even then, when I get home, I take the meat, prepare it for storage, and then use the bones for bone broth (more so with turkeys and chickens than dear, it's a matter of size) or tools or ornaments. A leg bone for instance can usually be salvaged for use in furniture or cookware, and boiling the bone sanitizes it for safe use.
Even in more day-to-day situations, you can still do a lot to minimize waste. I love to eat the seeds in cucumbers, tomatoes, and green beans, they're packed with vitamins and minerals. Some people, however, don't like to eat those seeds. That doesn't mean that you can't still utilize them instead of throwing them away. Planting those seeds can yield you a few plants, which you can use to grow more, saving you money and giving you the satisfaction of growing your own food. You can even sell those plants to people depending on where you live and what the laws are.
Beyond these ideas, there are many other things that can be done, including tanning of hides for use in making leather, or the twisting and drying of stems and vines to make ropes and such. Scrap strips of leather can be used for tie-downs or even hair ties if you're feeling rustic. When you set your mind to doing all you can to eliminate waste, you'd be surprised at just how much of the natural world can be recycled to minimize what you take.