Test things rather than only looking
Open every window and door, run taps, test extract fans, use sockets and check that locks and catches work. A visual walk-round will miss operational defects.
Inspect after rain where possible
Gutters, roof outlets, thresholds and external falls are easier to judge when water is actually moving.
A drawing can make a detail look settled before anyone has checked the existing building. Measurements, drains and structure still need confirming on site.
Look along rather than straight at surfaces
Low-angle light shows plaster ripples, uneven joints and poor paint preparation that may not be obvious head-on.
Keep a written list
Number each item, photograph it and agree when it will be corrected. A vague request to 'finish the snags' is harder to close out than a clear schedule.