Just a tip, I didn't get successful by ignoring 'low readings'. I got successful by ignoring the numbers on the VDI/VDU.
A dig all strategy can't be achieved on every trashy field, but over time on good sites you want to get to a place where you clear every nail. (takes over 10 years of gridding the same spot, over & over)
Digging all means a speeding up of your recovery time. (Recovery time to me means how quickly the trash get in your pouch after the first beep - it should be less than 30 seconds) This mean no getting on your knees, & no pin-pointer which both slow you down. I can expand my technique, if you wish?
Once you can do this then the next most important thing is to take Luck out of the picture by systematically Gridding (sometimes referred to as mowing the lawn) - We do this with flags spaced out every 30 metres. On ploughed land its easy to follow the lines.
Then grid on good land for as many days as the window allows - some can be very short due to the farmers cropping pattern & differing requirements. (always follow their rules which vary, so make sure you both know where to park out of the way & when NOT to be on the field, & most importantly you have no agreement in Law unless you have an agreement with what happens to finds from their land - our agreements are complex sometimes - as we are collector's not sellers)