I don't recommend giving this advice to people who are seriously depressed. Speaking as someone who went through that for two years, it's more of a disease than a lifestyle problem. I could have done all these things and still have been miserably depressed.
What helped me was talk therapy, medication (the biggest factor), and having really supportive friends.
What is the process of talk therapy? Isn't it just asking questions? Did I actually give any advice there?
For sure friends are best. But if someone vents online, how are we to know whether this person will go elsewhere or not for support? I'm not offering to take the place of a professional but I wonder if it really hurts to converse with a depressed person online by asking questions. Silence certainly isn't helpful. And if everyone just says, seek professional help, is that really empathetic? Sounds a bit robotic to me.
What helped me was talk therapy, medication (the biggest factor), and having really supportive friends.