A few things I can think of:

1. don't use the same password on your accounts

2. avoid public Wifis. If you do use public Wifis, VPN.

3. use 2FA whenever possible

4. use strong passwords, nothing identifiable to you (no birthdates, no pet names, etc)

But in the end, if the service you signed up for doesn't employ security best practices or saves your password in plaintext, there's nothing really you can do.