The biggest thing you can do by far to help the environment is what you eat. Eating animal products is the leading cause of carbon omissions, deforestation, animal extinction and ocean dead zones.
The other thing is what you consume. Unfortunately, today we are a throwaway society, we are taught to consume, particularly plastic products. Only around 6% of plastics are recycled, most people think because they put plastic in their recycle bin they are doing the right thing. The reality is most plastic still thrown away by councils. The best thing you can do is not use it in the first place.