I speak as someone who has been able to somewhat manage my own issues with depression.

• One immediate thing you can do is to cut out major sources of sugar from your diet. Give it 3 days (I notice the effects with less than 2 days) at least. Mental health and physical health are interconnected, so one bad thing affecting your metabolism is for sure going to have an effect on your brain (your brain's metabolism and ability to regulate energy too).
• Get enough sleep and exercise, as well as meditation. For meditation you can start with short sessions and make sure to keep in mind that there is no "failing to focus/meditate" as it's all part of the journey/process.
• As others have said, sunlight.
• Socialization. I personally don't get enough time out of the house but I notice the effects immediately when I do.

The next two tips are from the book "Feeling Good" by Dr. David Burns. I haven't finished the book yet but have made use of what I've read, and some that have helped me the most are:

• The "Self-Approval Method" - everyday, count the number of things you did or anything about yourself that you approve of or are proud of. Hopefully as you get more used to it that number will rise over time.
• The "Triple-Column Technique" - on the first column you will write down your automatic thoughts (the negative, self-defeating thoughts that seem to come naturally to people with depression); on the second column you will list down the cognitive distortions you can identify from the first column (look up a list of cognitive distortions, there are about 10 of them); and on the third column write down your rebuttal to the automatic thought but make sure it is realistic and not wishful thinking.

That's all I can say, and I hope you get better! All the best!