First, and the most important rule - just don't pollute the environment. We can divide it on some stages:
1. Throw away the rubbish in special area
2. recycle the rubbish ( burn, press, etc)
3. build more "healthy" factories, which don't pollute the air
4. eliminate "unhealthy" factories
5. make more events for cleaning rubbish
6. make a big fine for throwing the rubbish in a wrong area
7. start to do biopackages
8. make special areas for radioactive rubbish
9. дальше не могу