You can review the PRs and try to remove common errors before the devs check it. Then they don't have to correct the same mistakes again. I don't mean you do the corrections, you just suggest them to the PR authors so they probably won't repeat them again.
Common stuff like: - using latest eapi (at least for new pkgs)? - correct distfile name? - proxy maint project in metadata? - correct, sorted deps? - slot operators for rebuilds? - working tests if possible? - patches from reliable sources? - using || die after commands? - reusing eclasseses instead of custom solutions? - openrc/systemd done right? - is it secure? - you name it... :) Maybe we could script some of these to help too.