Kind of a general issue, but the plugin should follow the established WP Coding Standards, which provides general guidance for style, security, and performance.
Some things that can be addressed fairly quickly for solid gains:
PR #10 Addresses formatting and docs for a new baseline to work from. Once those are in place, it'll make it easier to make the other changes and to bring on other contributors.
Kind of a general issue, but the plugin should follow the established WP Coding Standards, which provides general guidance for style, security, and performance.
Some things that can be addressed fairly quickly for solid gains: