You can enable Automatic tags in the Zotero preferences. This will add any keywords supplied by the journal page as tags when you import using the Zotero browser connector. Beyond that, Zotero can’t do any other sort of automatic tagging at the moment.

+1 for this feature

Just the feature of automatically adding a "to_read" tag would be awesome.

+1 I use a saved search for untagged items.
As soon as I add the first tag the item vanishes.
With a default tag, I could use that for search and it would stay in the search result until I remove that tag to indicate the item is processed.

I thought about doing that as well, but it's quite cumbersome.

In case anyone is still looking for something like this, I made a small plugin called Zotero Tag Recommender to make tagging less tedious.
https://github.com/kinranlau/zotero_tag_recommender

While it doesn’t automatically add tags per se, it uses AI to suggest tags based on a paper’s title and abstract. It also takes your most frequent library tags into account so the suggestions better match your existing tagging style. You can then simply click to apply the ones you want.

It also supports multi-word tag autocomplete for manually adding tags. Unlike Zotero’s default first-word matching, you can type the beginning of any word in a tag (e.g. “gas”, “diff”, or “GDE”) and still match “gas diffusion electrode (GDE)”.

Hope it makes staying organized a bit easier!