There's a camp that you should not give unsolicited criticism. But sometimes problems that go unchecked can end up being your responsibility. How do you reconcile?

Three simple ways to phrase these things is:

• As a question: What if we ...? How about changing this to ...? Might X also work here?
• As a further improvement: This approach will work even better if we ... We could also do X here, so that
• Say it from the point of the team: all the use of 'we' in the previous items

Combining the three generally works best in my own experience.