Contact your legislators.
Legislators consistently indicate they want to hear from their consituents. Because of their time constraints, they will tend to ignore correspondence or calls from people not in their district. Use the tools on the right sidebar to learn your representatives' contact information.
Become more informed.
Delaware: Check out this graphic that illustrates how a bill becomes a law in Delaware.
Maryland: Review this simple illustration that consisely explains how a bill becomes law in Maryland's legislative process. In Maryland, the League of Conservation Voters has a Conservation Voter Report which gives you your legislators' green report. Complete the form at LCV Green Report.
Determine what is happening in your area. Pipelines (maybe not on the same scale as the XL pipeline, and compressor stations,) are being built in neighborhoods where they are unwanted. Contact your local reps - commissioner, council person, etc. Many have mailing lists; ask to be included.
Start local. Attend a school board meeting; attend a neighborhood association meeting.
Spend 30 minutes poking around and reading Skeptical Science.