The Better BibTeX Configuration can be found under the regular Zotero preferences pane, tab ‘Better BibTeX’.
The configuration of Better BibTeX is a little baroque compared to the standard Zotero Bib(La)TeX exporters (which only have hidden preferences). The defaults should just work, but here’s an attempt to describe what they do.
Making any change here will drop your entire export cache. This is usually not a problem unless you have a really large library, but you can read about what is involved here.
When merging items, also merge their citation keys into an bib(la)tex
When merging items, also merge fields that are understood to be CSL fields by Zotero.
When merging items, also merge their
When enabled, BBT will prepend the @strings section below to all Bib(La)TeX imports and will expand the strings during export.
When enabled, BBT will try to retain @string vars its exports unsurrounded by braces; when set to ‘detect’, single-word strings will be assumed to be externally-defined @string vars, when set to ‘match’, only @strings declared in the @strings section of the preferences will be preserved. If you don’t know what this means, leave it off.