Social media, emails, online petitions and even traditional letters don't influence our government in the U.S. nearly as much as we'd like. It turns out that phone calls are the most effective means.
If you oppose any or all of Donald Trump's policies you should take a look at this website:
5 Calls (5calls.org)
It couldn't be simpler. They tell you precisely who you need to call for specific issues and provide a script to read from. They couldn't make it any easier.
If you're not fully convinced, I strongly suggest looking at their about page. They explain why phone calls are the most effective way of seeking this change:
Calling members of Congress is the most effective way to have your voice heard. Call results are tallied by staffers and given to your representatives, informing them on how their constituents feel about current issues. The sooner you reach out to your representatives about an issue, the more likely it is that your voice will influence their position.