The best way to support survivors is to listen! Let them know that you believe them and are there to support them. Instead of telling them what to do next (filing a report, seeking help), remember it is their choice.
Do not victim blame. Victim blaming refers to questioning the actions of people who have experienced sexual violence, asking what they did, what they were wearing, etc. It discourages survivors from coming forward for fear they will be blamed, and can result in their experiences not being taken seriously. It also actively shifts the focus away from holding the person doing harm accountable.
If you're dating after experiencing sexual assault, or if your partner has experienced it, remember to take your time. Let the relationship progress slowly, and communicate in a way that allows you to understand and embrace your respective boundaries. Ensure your partner knows they're loved for their personality. Don't try to "save them", instead, accompany them and be patient, because there is no "right" way to start dating again. Give yourself what you, or they, need to feel safe, comfortable, and respected.