Note that although Strunk and White might have some reasonable advice on some topics, many of their recommendations are linguistically ignorant, just plain nonsensical, or violated all the time by excellent writers (including the authors themselves, sometimes on the same page they offer the advice). Here is a well-informed, highly negative review.

I very much agree with your advice about acting as a beta reader. It's really helpful for both parties and gets you lots of brownie points too!