What are best ratios to leverage debt WITHOUT OVER leveraging?

[Brandon Pace]

I just listened to BP podcast #424 and Jay indicated that the best way to make money during higher inflation times was to leverage debt. However, like many people have cautioned not to over leverage and take on too much debt. I am a new investor with 3 new properties and building my portfolio. I would like to get advice for ratios, rules of thumb, and best practices to steer me away from becoming over leveraged in debt, yet being aggressive in growth of portfolio. What advice could anyone lend me for debt utilization?