I think the most effective thing I've done to change the world for the better is being weird in public.
By weird I just mean being myself, which is considered weird in contrast to the status quo.
This might not sound revolutionary, but most of us have to wear a mask to survive in this world. For many of us it's a literal matter of life or death.
Me, I get a lot of protection from my privilege, so I see being weird as a duty, something I can afford to risk in order to push the edges of the envelope out for others who do not enjoy this security.
What makes me think this matters?
The effects are rarely direct, and they often cannot be measured for years, but now that I've been around for a half-century I've had the experience of learning that something weird I did in the past helped someone. In some cases it showed them that there's ways to live outside the default, in other cases it simply helped someone know they are not alone. In all cases it changed their trajectory, sometimes in microscopic ways (just a smile) but for others altered the course of their life and the lives of those around them.
I'm not trying to say that I specifically have some special ability to change lives, what I'm trying to say is that we all have this ability. Being weird in public might feel self-indulgent or pointless, perhaps even troublesome (it makes people uncomfortable) but I've learned that it not only feels good, it helps others feel good as well.
We all feel weird by the standards imposed by our society. This isn't an accident, it's a deliberate mechanism of control. If you can afford it, and if it makes you feel good, be weird in public spaces. You will enjoy it and you might just save a life.