To ensure consistency in Power BI visualizations, it’s important to establish a style guide defining colors, fonts, and chart types, and to implement shared datasets and standardized data models for uniform data sources. Using Power BI themes and templates streamlines design, while clear naming conventions for fields and measures promote clarity. Collaboration through workspace reviews and feedback, along with regular training on Power BI best practices, ensures cohesive and reliable reports.

To effectively bring your team member back on track, you need to discuss your concerns privately with the person. Be gentle but specific when pointing out the guidelines they are not following, and provide examples of effective data visualizations that follow the guidelines. Offer your support if they encounter any challenges in following these guidelines, and most importantly, create an environment where team members feel comfortable discussing the guidelines and suggesting improvements.

Communicate the importance of adhering to guidelines for consistency and clarity. Review the guidelines together, emphasizing best practices and why they're crucial. Provide constructive feedback on specific deviations, and offer examples of compliant visualizations. Engage them in a collaborative discussion to address challenges and tailor the guidelines if needed. Encourage open dialogue and continuous learning to foster adherence and improvement.

If you are the manager or team leader it's important that you lead in these instances: By the time you see symptoms like "straying", it's really just an indicator that your standards are not mandatory, important and created for a reason. To tackle this specific instance, I'd recommend to discuss it in private with the team member; listening and understanding the why and explaining (and reinforcing) why the standards exists. If they bring up good points for why, you should invite them to update the standards in a forum of their peers. For the long term I have found that having a daily design review with my team, where everyone provides feedback helps. It makes everyone invested and allows everyone to contribute equally.