You can't really avoid toxic people, because they're everywhere and it's not always easy to identify them quickly. But if you have good boundaries, and are willing to say no to them consistently, you can prevent them from becoming important to you and messing up your life. Often when they discover they can't become dominant over you they will move on to easier targets.
It's sometimes easier to tell if someone's toxic by watching the way they treat other people than by evaluating their interactions with you. If someone is treating others in ways that make you uncomfortable, it's a good idea to keep your distance from them.