Talking about effective altruism with coworkers can be really awkward. There's potential to come off as "I'm more moral than you", potential for "I think the charities you do support are useless", for "I'm so rich I can afford to give away lots of money", "I'm trying to convert you", "I think you're a bad person because you don't do this", and for just seeming weird. Most of the year I just don't bring it up, but as we get into giving season I feel like I ought to try.
I think most of the social difficulty around effective altruism comes from the demandingness aspect, the idea that to be a good person you should be devoting a substantial effort to making the world better. One way around this is to mostly focus on the effectiveness angle, saying "here's an awesome charity that can do huge amounts of good with your donation". The best charities are so much better than the rest that pushing effectiveness seems well worth it, and any sort of discussion of giving helps normalize it and lead people to give more. So here are three ideas for promoting effective giving among your coworkers:
Matching Donations. Offer to match donations to one of GiveWell's picks. This provides openings to talk about effective altruism, why evaluation matters, and the good this charity can do. Lots of people are more willing to give if they see the people around them are giving too.
Donation Drives. Many workplaces traditionally have donation drives around the holidays. If your work has one, consider getting involved and helping out. This can then let you push some for effectiveness as a consideration in choosing what charity to raise money for. If you don't have one yet, or the one you have is tightly coupled to an existing charity, like collecting cans for a foodbank, then consider starting a new one.
Updated Recommendations Discussion. GiveWell will be putting out their updated recommendations by December 1st, and judging from their recent blog posts there are likely to be several new top charities, each presenting different benefits and tradeoffs. Hosting a discussion to talk about these new options when they come out is a great opportunity to get into ideas about how to choose a charity and what matters.
I hosted a recommendations discussion last year and this year I'm doing that again plus getting together with some other EAs here to match donations. I haven't tried organizing a donation drive but it seems promising.