Leaning using EGT - Lycoming O-540 (Aztec)

On my first flight in the Aztec with a fellow pilot who was doing the
flying, he stated to lean using the EGT (a recently installed
Electronics International digital single probe device)to circa 1300 and
no higher than 1350.

The aircraft does not have a CHT.

I am totally new to operating larger engines like the O-540 (no fuel
injection here) and want to ensure I dont damage anything. I hear a lot
of talk and hearsay about LOP/ROP leaning procedures.

Like most owners, I want to operate my aircraft efficiently, but not to
the detriment of engine reliability.

Any advice is welcome.

Regards,

Dean