What issues are you dealing with (if you feel like sharing)? I can speak from my experience being in therapy for AuADHD, anxiety, depression, childhood traumas, and a few other things.

ETA: Some generic things from my therapist that will help most people:

• Drink enough water. This alone can have a significant impact.
• Try to do regular physical activity that you enjoy, if possible. Even if you don't feel like it.
• Check your posture. If you find yourself hunching, try fixing that.
• Do things that you know that you enjoy when you are not depressed, when you are depressed. Our brains are weird and "fake it 'til you make it" kinda works - by doing non-depressive things, you can trick your brain into being happier.
• Try to engage socially, if you find yourself to be a hermit. Our brains are evolved to be social animals and isolation can be damaging.
• If you are having trouble with the state of the world and things that you do not have control over, try engaging in things that you do have control over. This can be as simple as deep cleaning your sink or fixing a squeeky hinge. The amount of frustration caused by inability to impact important global happening is problematic for maintaining good mental health - our brains evolved in environments where life-threatening problems had immediate solutions but humans have built societies that don't work that way.

Important items

• Be patient and kind to yourself. Especially your past self. We all did cringy things when young with brains not fully-developed and/or without the information that one has currently. If you have trouble doing so, try mentally taking a step back and pretending that you are dealing with a close friend who you care about deeply. Would you judge them and make them feel bad about their past mistakes? I hope not.
• Concern and depression about the world at large is a very valid way to feel. It's important, especially for those of us with mental health challenges, to take the airplane safety spiel "put your own mask on first before helping others" approach to rendering aid to others. If you are in or near crisis, you are not in a place to help others and need to focus on getting to stable ground yourself first. Needing to do this isn't slacking off or "not doing your part". Not everyone is equipped to be out marching all the time (some are not equipped for this at all). If someone offers unhelpful criticism of inability to engage physically due to mental or physical health, they are best ignored rather than responded to.