Consider your audience. I recently saw the discord discontinued their light theme, probably because it wasn't being used much and was causing bloat. However, older folks who are working to being in excel and Microsoft word, are most likely going to hate your dark theme.

Consider your environment. Are people staring at the screen for long periods of time with dense data, dark themes can be less straining on the eyes. Are they ever going to be using the application outside in the sunlight, dark themes are super hard to read in the sun.

If you're going for accessibility, light theme first, then develop a dark as an alternative.

And if it's an MacOS app, please make dark theme configurable outside of the system configuration!!!

I forgot someone posted this video awhile ago, but he talks about how light effects typography, really interesting, incredibly nerdy https://vimeo.com/70414929

Also, this is pretty interesting detail: "White also reflects all wavelengths of light. Because the words and letters in paragraph text are compact and close together, when white text reflects light, the reflected light scatters and runs into neighboring words and letters. This makes the shape of the words and letters harder to perceive, which affects readability. Compare that with black text, where the black absorbs the light around each word and letter, making them easy to distinguish." src: http://uxmovement.com/content/when-to-use-white-text-on-a-dark-background/

MailPlane has a nice case study on the unexpected design considerations they encountered when supporting dark mode.

https://mailplaneapp.com/blog/entry/designing_dark_mode_for_mailplane.html

The best thing in fact is having experience in living with dark mode. Try to use it for all your apps and sites on daily basis. For web Dark Reader extension will help a lot

https://www.toptal.com/designers/ui/dark-ui

https://tubikstudio.com/light-and-darkness-in-ui-design-matter-of-choice/

https://tubikstudio.com/dark-side-of-ui-benefits-of-dark-background/

https://tubikstudio.com/light-or-dark-ui-tips-choose-proper-color-scheme/

https://shakuro.com/blog/in-the-dead-of-night-why-we-are-drawn-to-dark-interfaces/

https://medium.com/envoy-design/how-to-design-an-accessible-color-scheme-4a13ca12c92b

https://medium.com/@erikdkennedy/color-in-ui-design-a-practical-framework-e18cacd97f9e

This is purely subjective, but have a look at the way the Things 3 app does it. By far my favorite app dark mode.

Consider that your users may use nightshift/f.lux because they don’t want to look at blue light in the evening. I also found that especially dark blues tend to look very different with those modes enabled. It really becomes greenish, even when you’re used to the white balance shift.

You can have a look here:

https://www.carbondesignsystem.com/guidelines/color/overview#dark-themes

It is not as accessible for some sight-impaired individuals.