Visit these parks. If you ignore them, they will go away.
Report littering. Call the Long Beach Parks Department at (562) 570-3100. Yes, they DO want to hear from you!
Join a Coastal Cleanup. These occur at nearly all the parks described in this site. The beaches have cleanups at least once a month. At the very least, people who watch you pick up litter will think twice about their trash. The Parks Department runs a number of clean-up, tree-planting, and restoration activities throughout the year.
Garden wisely. Use native plants (or at least, native-friendly plants), which require very little fertilizer, pesticides or water. A list of plants for the Palos Verdes Peninsula has been developed by the California Native Plant Society--all these plants are suitable for Long Beach as well!
You can purchase native plants from these sources (at least, at certain times of year).
Be a responsible pet-owner. Snip snip snip. Scoop scoop scoop.
Join an environmental group. Here's a list of great organizations that are helping out in Long Beach.
Be a good citizen. Vote. Call/write/email your elected officials (senate representative governor state assembly state senate city council mayor) and the newspapers (LA Times Press-Telegram The Grunion/Downtown Gazettes The District), as well as local blogs LBReport Long Beach Politics.