In addition to on-going code review I would consider:
Existing code audit(code review)
Code review is normally done for new and changed features. Based on what you have already found I would take a step back and review all the existing test code as if it is new. You'll often need to develop a strategy to review them in chunks alongside existing feature development.
Champion good practices
If you document, promote and encourage good practices they are more likely to be followed.
Red, Green, Refactor
Learn about and practice this technique.
From lunch and learns to half-day seminars provide plenty of learning material on doing the right thing.
Pay for performance
Include code quality items in personal performance reviews. Reward the bottom line ($) for doing the right thing.
Tech Debt weeks
Much as I try to do the right thing now I also balance this with the business need to deliver features. My outlet is that I sometimes create debt tech tickets. We do 1 or 2 weeks of tech debt every 6 weeks so these are not 'wishful' tickets that aren't ever done but actually queuing up of real work to be done soon.
From dev-dev to dev-qa to qa-qa it helps to keep folks more honest, open and questioning assumptions. Group-think can be an issue but generally I find the benefit to be positive.
Code Quality Tools
From code climate to codecov there are a lot of code analysis tools out there. They help you manage the process of having quality code by analyzing your code base and test coverage. They can show you improvements over time and can let you set and manage levels of code quality.
Test your tests
Consider adding code that looks at the structure of your tests themselves and looks for things like: duplicate page objects, unused page object, not using page objects, use of
true == true statements, etc. Make these into actual tests so that you can let the tests help enforce the standards, not you through constant persuasion arguments in code review.
btw 'industry standard' doesn't work for me here. The software quality industry is still too varied and undefined.