The biggest helper for me when trying to read other peoples' code is having a document (or documents) which describe what the heck the code is supposed to be do

The biggest helper for me when trying to read other peoples' code is having a document (or documents) which describe what the heck the code is supposed to be doing in human terms. This is especially true when I'm not super familiar with the business history, long forgotten bug fixes, and nuance which was previously worked around or implemented. Software documentation almost always sucks, in my experience. When I do find well written documentation that reflects the code, it becomes much easier to understand the code quickly so that I can make the changes I want to make. But nobody likes writing documentation.