If you want to be an ally to trans people, you need to not only support trans liberation politically, but you also need to support the individual trans people in your life. Unfortunately, a lot of cis people don't really now how to best support their trans friends. So here is a very brief list on how to start doing that.
1. Respect a trans person's name and pronouns
I can't stress enough how important names and pronouns are to trans people. It's okay to mess up once or twice, but past that, it's really unacceptable. Yes, it can be hard, but it's essential work if you want to support trans people.
2. Don't ask invasive questions
Pretty much every trans person has had an experience with a cis person asking them invasive questions about their identity. This experience is always humiliating and uncomfortable, so absolutely just keep your questions to yourself (unless you were explicitly told that it was okay).
3. Don't ask them for their coming out story
I've had experiences with cis people who feel entitled to know my story. The problem is my story with coming out was actually pretty traumatic so I'm not really interested in sharing it on a whim. If you're trying to be supportive, don't ask about potentially painful memories.
4. Don't shame them for not "passing"
Several of my trans friends have had experiences with cis people who think they're doing them a favor by telling them they don't "pass." The first problem with this is that it assumes that "passing," or looking cis, is something all trans people should aspire to. The second is that telling a trans person they don't "pass" is basically saying you don't see them as the gender they are presenting as, which is very invalidating.
5. Absolutely do not out them
"Outing" refers to telling other people about a person's trans status before you are given consent to. It is something you should never, ever do. It doesn't matter what your relationship to the person is, this is their story not yours. Plus, outing a trans person can even be dangerous.
6. Don't be ashamed to be seen with them in public
This might seem obvious, but I've found that for many aspiring cis "allies," it's not. A lot of times, cis people want to tell trans people how much they support them, but their fear of being judged prevents them from actually interacting with trans people in public. This is of course very superficial support, and isn't really meaningful.
7. Check in with your trans friends
Being trans is really hard and it often takes a toll on our mental health. Forty-one percent of trans people attempt suicide which is significantly higher than the national average. This makes it very important to always make sure that your trans friends are safe.