When to replace road tires for new?

Is there a general rule of thumb to replacing road tires? Mileage, et..is there a recommended tire? There are so many types, I am a recreational rider averaging 150 miles per week.
Thanks :rolleyes:

Some tires have wear bars ... other than that, as a recreational rider, once I get one flat, when the tire is off it's easy to feel the tread thickness and make a decision as to whether there's enough left to keep it on, or replace it. If you start getting flats more often than usual that's a big clue.

Then there's dry rot and cracked sidewalls for tires that lie around more than they get ridden, but at 150 mpw you're not going to be seeing those. :)