The jargon of an environmentalist generally revolves around two words, understand and protect. It is not difficult to comprehend the meaning of these words; they simply mean that human beings have to understand the importance of the environment, and take necessary measures to protect it. If you do not understand the environment, you will never realize how brutally it is being affected by human activities, and hence you will not think of protecting it. The environment is characterized by biodiversity, which is responsible for maintaining a state of equilibrium in the environment. Loss of biodiversity will eventually trigger an ecological disaster. Thus, its preservation should be one of the (if not the only) goals of mankind. Here's how it can be done.
Distinguish Between Need and Greed
What drives a human being? The answer to this will be very subjective. I believe that man is driven by either his need or his greed. The greed of mankind has taken a toll on the environment. Many species of plants and animals have fallen prey to this greed. There are several products made from plants and animals. Before buying such products, ask yourself; do you really need such products? By using only the products that you need, you will reduce the demand for several animal and plant products, which will eventually stop the manufacturing of such products, and thus save numerous species of plants and animals.
Go for "Green" Products
There are various companies which use a manufacturing process that does not harm the environment. Go for the products made by such companies. This will motivate other companies to implement environmentally friendly techniques to the production of their products. Prefer local market products, as transportation of products from distant markets contribute to environmental pollution. Encourage organic farmers by buying fruits and vegetables from them.
Note: If possible, research on the Internet to make sure that the eco-friendly claims made by the companies are genuine.
Avoid Invasive Species
People want their garden to be unique, so they prefer exotic species like trees and plants in their garden, and thus neglect the native species. Your favorite exotic species may turn out to be invasive, and might hinder the growth of the native species. In order to preserve biodiversity, it is important that you promote the growth of native species. Invasive species are not restricted to plants, invasive species of animals (translocated by humans) may also become dominant, thus resulting in the decline of the native species of animals.
Try to Minimize Pollution
The alarming rate of global warming will eventually result in climate change, which might make it difficult for certain endemic species to survive in their natural habitat, and this may result in their extinction. So, it is essential to try avoiding any activity which directly or indirectly increases global warming, or results in any damage to plants and animals (aquatic, terrestrial, etc.). I know it is difficult to completely avoid pollution, but you can surely do your bit to minimize it.
The first thing that might come to your mind when you think of preserving biodiversity might be to save the forests! I agree with you, and I also believe that minimizing deforestation can be a major step in conserving biodiversity, but it is very difficult to check deforestation from your home. If we want to tackle deforestation, we have to rely on afforestation, which is a process that can take years to bear fruit, but will definitely be worth it.
Finally I would like to say, do not be cynical! Believe that you can make a difference. Small initiatives taken by you can have a major impact! The environment was not damaged in a day, so you cannot expect it to recover in a day. Only persistent efforts can save our environment! Let's do what we can!