Here’s a usable list, and it is almost the same for surgical wounds and dressing changes.
Contact your surgeon if the drainage coming from or around the incision increases, or becomes thick, tan, green or yellow, or smells bad. That last cluster means pus.
Four things, then. More of it. Thicker. A color from that list. A smell. Any one of them counts; they do not have to arrive together.
With wet-to-dry dressings there is one more, which is about time rather than appearance: contact your provider if drainage is not decreasing after 3 to 5 days.
Drainage is rarely the only thing changing, so look at the wound alongside it: worsening redness, more pain, swelling, bleeding, a wound that is larger or deeper, and a wound that looks dried out or dark. For a closed surgical wound, a temperature above 100°F (37.7°C) for more than 4 hours is also on the list. That figure belongs to closed surgical wounds; other wound types have different figures.
This answer can’t describe normal drainage in any detail, though that is what most people want to know. The practical substitute is a baseline of your own: knowing roughly how much the dressing was absorbing and what color it was last week is what makes increases visible.