One cannot miss what one does not know exists.
A book by Michelle Nijhuis, Beloved Beasts, Fighting for Life in the Age of Extinction, presents several classic examples of animal species severely affected by human activities. Michelle describes animals which became symbols of conservation. Many such species are still with us, while some can only be seen in the natural history museums.

We all heard of the Wild West and the American Frontier, and the decimation of the bison (the American buffalo). We also heard how excessive use of pesticides, one of which is DDT, decimated many bird populations, including the hawks and the eagles. Over several years, the fashion industry dating back to the late 1890s slothered countless shore birds, with near extinction of the whooping crane. Poaching and trophy hunting in Africa led to extinction of the black and northern rhinos. The examples keep on pouring in. Michelle Nijhaus describes those stories beautifully and in great depth.
We do not know precisely how many animal species inhabit the Earth, as current estimates are vague. We are much better at counting large land animals, such as the elephants or rhinos, but we are pretty bad at estimating anything else.
How do we protect anything, without knowing that it is there?

I think that we do not need to classify all the species to begin to understand what to protect and how to protect them. Protecting habitats can often be more effective.
After reading the Beloved Bests, I realized that I must agree with the statement that we need to protect what is common, while it is common. It is not a novel idea, but in my opinion critical. Such early actions may seem as trivial and unnecessary endeavors, but they are the key to future successful conservation efforts.

We should also note that as we establish safe havens for many endangered species, we are also protecting common species. If we start to protect more common species, we will preserve biodiversity. As greatly noted, the planet requires preservation of complexity. For example, countless grass lawns do not provide any diversity of plants and insects, they are simply green deserts. Rather than grass, plant naive flowers.
The real dilemma is that we already have countless species with dire futures. In order to protect the Earth’s biodiversity, we have to protect them before their numbers begin to drop. This approach not only preserves the species, but also maintains their genetic diversity. Within species, genetic diversity is critical to their survival, and should be emphasized in any conservation effort.

What the book by Michelle Nijhuis made me realize is that conservation does not exist in a vacuum. Animal protection laws, without infrastructure to support the local human communities will likely fail, and many failed in the past. For example, attempts to create national parks in parts of the African continent ignored the needs and voices of the local communities, many of which saw this as another attempt of colonization. Some even killed rare animals in the established parks in protest. Making the local communities involved in conservation can drastically change the course of many species. This is true all over the world.
I do not have all of the answers, but we have to protect what is left as a society. Even I can think go simple things that anybody can do: use less plastic; conserve water; plant wildflowers and native plants instead of grass; do not use pesticides, insecticides, and herbicides; recycle; conserve energy; support conservation efforts; donate to local rescue groups; leave water for wild animals during heat waves; do not plant invasive plant species; do not release invasive animals into the wild; bring your own shopping bags; do not buy synthetic clothes; and many other simple lifestyle changes.

One particular example we can try to address is missing plastic toys. I love to walk on the beach in the afternoon, once the masses of beachgoers begin to depart. I always thought that the beach would be mainly full of plastic bottles, and they do appear, but what I see most is plastic toys.
Children love to dig in the sand right by the water, at least I did. As the waves approach the shore, their power washes off the toys, and buries them in the sand. Keeping track of toys is challenging. To make you realize how many toys you are missing try this exercise. Number the toys your child takes to the beach, and count them again before you leave. I bet you will be missing at least one or two. Many times I would toss abandoned toys deeper into the sand, but once left they become garbage. Save the beach and save your money by counting the toys.
Although we need more global changes, you are the first step to conservation. Your next step is your voting poll, but I will leave that argument for others to make.