The UNESCO Institute for Statistics estimates that only around 30 percent of researchers worldwide are women. Similarly, according to the Economics and Statistics Administration of the US Department of Commerce only 24 per cent of STEM jobs are held by women, with individual disciplines like Engineering having a significantly worse gender bias. There’s also extensive literature on biases against women in STEM, affecting all aspects of academia, including hiring, publishing, citation counts and teaching.
Given these disheartening statistics, it is clear that there is still a long way to go before we can even start thinking about gender equality in STEM. Why is it that I, a man in STEM, am writing about this? Because to me these statistics also show another thing: men, who are dominating these fields, have an obligation to support women in STEM and help level the playing field. But how can men help to facilitate change and support women in STEM? All the things I try to implement are the result of listening to women—who sacrificed their spare time to educate me—and taking their advice. Thus, maybe the single best, most actionable thing is this: step back, shut up, give women space, and listen to them.
What can this look like on a more concrete level? Ask yourself about your own environments: is it men, including me, who are taking up all the airtime at meetings? Chances are that this is the case, as women are interrupted more often than men and speak significantly less at professional meetings. So take a break and let others speak. To whom are you paying attention? Is it the always same male crowd? For social media, some tools let you check the gender breakdown of the people you read. Make sure to identify those voices you’ve ignored so far and listen to them. Along the same lines, ask to whom you are giving an audience. Make sure also to boost the messages of women instead of only focusing on your (male) buddies. Generally, the male overrepresentation in STEM means you’re likely to default to male perspectives. Make sure to steer actively against this.
This becomes even more important in the context of organizing conferences, events or communities at large, as representation matters. Achieving a 50:50 gender split at conferences is still not a given and is the sad reason why #YAMMM (yet another mostly male meeting) and #manel are common hashtags on Twitter. Try to consult speaker databases that relate to your topic of interest (like the Open Speakers Database  for all things open). Additional ways to counteract gender-biased presenter lineups are listed in Ten Simple Rules to Achieve Conference Speaker Gender Balance.
Furthermore, look at who is participating not only at your co-organized conferences, but also at your communities at large, be it a research project or a lab you are running. Do you end up having a homogenous, male participant base? This might be because the community’s culture and behaviour are all but inviting for anyone else. Formulating well-stated, positive community values along with a code of conduct can help with a cultural change. The Diversity, Equity, Inclusion report of OpenCon offers excellent guidance and lessons learnt on these topics. Kirstie Whitaker gives a good example of a code of conduct for the lab. Lastly, you will need to enforce your code of conduct and reinforce good behavior in your communities, as only this will lead to lasting change.
If you are not the one setting the official rules for the communities you are involved with, you can still play your part in supporting women in STEM. Ask the organizers about their gender balance amongst the presenters and decline the invitation if it is a manel or YAMMM. Be explicit about your reason for declining  and ideally even offer them a list of women they should ask to present. In my experience this can often have a direct effect on who will speak at an event.
You can similarly push conference organizers and project leaders to adopt a code of conduct if they haven’t done so already. And lastly, there is an opportunity for you to speak instead of listen: it is important that unacceptable behaviour should be called out by everyone, not only the targets of it, especially as men face fewer negative consequences than women for doing so. So, step in when you observe inappropriate behaviour as well as sexist jokes and assumptions. It is what Mikka McKinnon pointedly called Intervene when you see BS. Don’t be quiet in these situations, but speak out and offer support.
This is by no means a complete list of things that men can and need to do to support women, inside and outside STEM. It does not magically solve all structural biases inherent in the current STEM environment. But I believe it makes for a good start for improving oneself, including me: take some steps back, listen to women who have all the unwanted experience in how STEM fails them, and learn how you can make a difference. Only then can you help the world of STEM to become a better place for all.