Nice you do these types of guides 
The first thing I typically do when reviewing patterns is use Unificator (snap on "Vertices and Sub-Part Vertices"). For a file without ring primitives, this should not yield any results. Together with the Edger2 technique Magnus mentioned, you get a good impression of vertex mis-matches.
Another thing to mention:
For printed parts appearing in transparent colours, all non colour 16 lines should follow a "0 BFC NOCLIP" line, like here: https://library.ldraw.org/parts/2210
If the part is not done this way, it will not display correctly.
Regarding colour checking, it can be helpful to inline all sub-files then sort by colour (make sure "ignore structure" is checked). I find it easier to get an overview of which colours a file contains this way. Sometimes you will encounter colours that are hard to distinguish by eye view only, so sorting helps. I would encourage part authors to already structure their files so that colours are already sorted, but it's not always the case or sometimes not possible.
Common colour-related errors:
-sub-file uses a similar, yet different shade when they actually should be completely identical
-Metallic colours should only use "Metallic" type colours (80 for Silver, 82 for Gold, 300 for Copper, 316/87 for Dark Grey/Titanium/Gun Metal, 10045, 10049). Chrome (except mirrors) and Pearl colours are never used on patterns.
-a part of the pattern which should be the base colour 16 is hard-coded to something else
The first thing I typically do when reviewing patterns is use Unificator (snap on "Vertices and Sub-Part Vertices"). For a file without ring primitives, this should not yield any results. Together with the Edger2 technique Magnus mentioned, you get a good impression of vertex mis-matches.
Another thing to mention:
For printed parts appearing in transparent colours, all non colour 16 lines should follow a "0 BFC NOCLIP" line, like here: https://library.ldraw.org/parts/2210
If the part is not done this way, it will not display correctly.
Regarding colour checking, it can be helpful to inline all sub-files then sort by colour (make sure "ignore structure" is checked). I find it easier to get an overview of which colours a file contains this way. Sometimes you will encounter colours that are hard to distinguish by eye view only, so sorting helps. I would encourage part authors to already structure their files so that colours are already sorted, but it's not always the case or sometimes not possible.
Common colour-related errors:
-sub-file uses a similar, yet different shade when they actually should be completely identical
-Metallic colours should only use "Metallic" type colours (80 for Silver, 82 for Gold, 300 for Copper, 316/87 for Dark Grey/Titanium/Gun Metal, 10045, 10049). Chrome (except mirrors) and Pearl colours are never used on patterns.
-a part of the pattern which should be the base colour 16 is hard-coded to something else