Two things that I think about prioritization; and my perspective here is, as usual, one that takes language diversity into account:
* Help people who look for stuff. Understand why do they look and how do they look for it. The mostly-simple assumption is that most people look for stuff because they need it for school or college homework, because they need it for work, or because they heard about it on the news and became curious (this includes interest in pop culture, music, movies, etc.) This is mostly relevant for cultures the language of which is stably spoken by many people and used in education and media. Students usually search the web for homework in the language in which their teacher gave them their homework; people in general search the web in the language that they use in their workplace or that they use on radio, TV, newspapers and other websites. We need to be there for these people. We are already doing it quite well in some languages and we must not neglect them, and we are doing a bit less well in some others, and we need to improve.
* Help people who want to look for stuff, but do not or cannot. This is a very wide area that we cover badly or not at all, but we should. There are a lot of possible reasons for this. Some people are just too busy earning basic living and don't have time to learn, even though they possibly want it. Some people (a lot!!) live in cultures where no kind of education is accessible at all, at least not the kind to which we are used to in The West—public schools, colleges, libraries, etc. Some people can only access education in a language that is not their own. Some people read books and newspapers in their language, but don't have keyboards for it, so they don't use it online, and think that the web can only be used in foreign languages; some of them are lucky and know these foreign languages, and some don't. Some languages just never had any kind of support from governments or cultural institutions (and some of those are spoken by millions of people!). And so on. We need to be there for these people, too. I'm not saying it's easy; it isn't. It's super-difficult. It's probably beyond Wikimedia's current practical capacity and resources, and can be done in very small steps. But I am saying that it's necessary, and that at the very least we must not forget that BILLIONS of such people exist, and that our movement's and organization's motto includes the words "every single human being".
How do I prioritize? If I can do a small thing for the second group, I do it. A small thing I can do for the second group can help a volunteer to do a lot of things that I cannot. If the thing is bigger than my capacity allows, I acknowledge it. It's more principle than method, but it's something.