I know just what you mean when you say that “enjoying” nature is not enough. There’s nothing better than a “mission”, a sense of being able to contribute something really useful.
@lothlin’s advice about striving to take good quality photos is excellent. iNaturalist and the web in general are overflowing with photos, but ones that are really “good” are an absolute rarity… by “good”, I don’t mean artistic, or even technically perfect, but images which simply and effectively “describe” the characteristics needed to ID that particular organism. It’s a tough task, as paradoxically you often first need to know which features are important, but over time, you build up a sort of sixth sense.
For example, a fun and useful personal project could be to take a look at @lothlin’s Layman’s guide to fungi (or other similar) and see whether you would be interested in taking photos to illustrate some of the traits she describes.
Finally, I know your question refers specifically to making observations, but something really useful you could contribute to iNaturalist would be to also start identifying other people’s observations. There’s an enormous backlog and with the current ratio of observers to dedicated IDers, it risks growing exponentially over the next few years. You could try high level IDing of “Unknowns” or at phylum level, and/or study a category you’re particularly interested in and start IDing to finer taxonomic levels in that field. Just an idea 
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P.S. No idea why this came out as a reply to lothlin (or to myself!), it was intended to be general. Sorry for the chaos.
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