In the aftermath of Donald Trump’s election, a lot of Americans are looking for new ways to make a difference and do their part to stop what they consider a dangerous agenda. And some are hoping that their representatives in Congress can act as a check on Trump.

For those taking this approach, blogger Emily Ellsworth has some advice: Don’t just tweet, write, or email your representatives. Call them — and go to town halls.

In a series of tweets, Ellsworth drew on her experience as someone who worked in Congress for six years to note what works and what doesn’t:

I worked for Congress for 6 years, and here's what I learned about how they listen to constituents. — Emily Ellsworth (@editoremilye) November 12, 2016

First, tweeting or writing on Facebook is largely ineffective. I never looked at those comments except to remove the harassing ones. — Emily Ellsworth (@editoremilye) November 12, 2016

Second, writing a letter to the district office (state) is better than sending an email or writing a letter to DC. — Emily Ellsworth (@editoremilye) November 12, 2016

But, the most effective thing is to actually call them on the phone. At their district (state) office. They have to talk to you there. — Emily Ellsworth (@editoremilye) November 12, 2016

We repped half a million people, it was impossible to read and respond personally to all letters. Impossible. — Emily Ellsworth (@editoremilye) November 12, 2016

This was something in particular that I cared about as a staffer and worked very hard on, but the sheer volume of emails is overwhelming — Emily Ellsworth (@editoremilye) November 12, 2016

So, we batched them with computer algorithms and sent out form letters based on topic and position. Regardless of method received. — Emily Ellsworth (@editoremilye) November 12, 2016

But, phone calls! That was a thing that shook up our office from time. One time, a radio host gave out our district office phone # on air. — Emily Ellsworth (@editoremilye) November 12, 2016

He was against our immigration policy and told our constituents to call. And they did. All. Day. Long. All I did all day was answer phones. — Emily Ellsworth (@editoremilye) November 12, 2016

It was exhausting and you can bet my bosses heard about it. We had discussions because of that call to action. — Emily Ellsworth (@editoremilye) November 12, 2016

The basic lesson: Tweets, Facebook messages, emails, and even letters can be easily discarded and ignored without much disruption to a congressional staffer’s day. But a blast of phone calls can seriously disrupt a congressional office, leading them to at least openly consider and discuss the issues you’re raising.

Ellsworth also cautioned that, generally, these messages only fall to staffers — not the member of Congress you’re trying to reach. If you want to get more direct contact, you’ll probably have to go to some sort of public event, such as a town hall.

We held town halls consistently that fewer than 50 people showed up for. And it was always the same people. So, shake it up. — Emily Ellsworth (@editoremilye) November 12, 2016

So there you have it. If you want to make a difference, call your representatives and show up at their town halls. For more information on how to do that, check out the websites for the House of Representatives and Senate.

Watch: It’s now on America’s institutions — and Republicans — to check Donald Trump