Yesterday, I attended a 6 hour grammar refresher course run by the Society of Editors (Vic). I grew up in a time where grammar was not formally taught and my grasp of the rules is intuitive rather than anything else. I can usually get by, partly from practice, partly by ear.
Most of the attendees confessed to similar issues...we are able to recognise something as being wrong but have not the language or analytical skills to deconstruct the actual fault.
It was an intense time. Sooo many grammar rules (and exceptions), so little time. But Glenys Osborne our tutor powered through and by the end of the day we were all reeling.
Time to disappear into the stimulus-free room and let the refresher sink in. The notes, examples and worksheets might help too. The day-long course probably could be expanded to at least twice that without running out of material. And that's with people already working intensively with the language as writers and editors.