1. Call a state or district office first.
2. Leave a voicemail. If voicemail is full, press "0." This will typically connect you to a receptionist who may be able to take your message or transfer you to a voicemail that isn't full.
3. Call the national office, if you can't get through. Or to see if you can get a real person.
4. Be prepared to give your name and your location. You can refer to yourself as a constituent, as per the script, and they might not ask.
5. Note that the operator is likely using some kind of form to mark your call, the goal is to generate a high volume of calls that require the operator to check off individual boxes. That means it’s critical to name your issues specifically and not just say something like "oppose Trump."
6. Read this set of tweets for more on why these calls work.