Start here: https://forum.inaturalist.org/t/useful-inaturalist-tasks-for-non-experts-wiki/35034/ and https://forum.inaturalist.org/t/in-need-of-your-mentorship-knowledge-coaching-new-members/33371
I definitely echo the advice to focus on your home county/state/province first and expand with more experience. For example, I have 45,000 identifications in New Mexico, or about 1/3 of my time on iNat.
The unknown ‘pile’ is a great place to practice sorting.
Next, you can pick a plant or animal group you’re interested in and review common species. Helianthus annus in North America - common sunflower - is a good one where you’ll learn what to look for in the flowers and leaves and which other species are commonly misidentified. Find resources like field guides or keys that you can cite if users have questions.