One of the most helpful ways I've learned to support friends is by offering specific, practical help. When someone is going through a difficult time, it's often hard to know how to offer support or what to say, so people default to phrases like "let me know if you need anything." While this is done with good intentions, when someone is struggling, they're usually not in the right mental or emotional space to have the capacity to figure out what they need or to reach out and ask for help. I've found that it's much more helpful to take the initiative and offer to help with daily tasks instead. Doing things such as dropping off a meal, offering to help take care of their pets, or simply checking in now and then makes support feel more accessible. These small gestures help take the pressure off of the person who's struggling and can bring a small sense of relief during an otherwise overwhelming hard time.
I have learned to say less and listen more. Many times people just want to be understood, they don't want advice, they don't want personal examples, they want to just be heard. When a friend is struggling I find it helpful to flat our ask them if they want to vent or if they want help thinking through their next steps. Often friends just want your presence.