What is the best technique to improve removing PETG from the print bed?
Correctly level your bed. Seriously, that's the answer. PETG does stick well, but it only gets difficult to remove if you're smashing the first layer against the bed with a nozzle that's way too close. With the bed leveled properly - using feeler gauges or test prints and a sub-0.1-mm-precision caliper - I have no trouble taking PETG prints off a buildtak-clone bed. Glass should be easier.
If you already have PETG stuck to a build surface you care about and don't want to risk destroying it, try heat, or alternating heat and cold.