Olin has a lot of experience similar and different to mine and I don't agree with all he said, but that's just his opinion.
I know there are standards for capturing Logic Diagrams ( which includes Analog but means a logical capture vs a physical capture, but I've forgotten where.
But since standards aren't free, few small shops buy them, just like IPC standards for layout design pads, spacings, design rules, quality criteria, so beginners learn rules from whoever they work for.
Historically, military created standards for schematics with dots on all junctions and no 4 way junctions because microfiche was used for archive storage and dots could appear on cross lines would be ignored from lens blurring. But those are rules based on old technology.
I can read any good schematic, no matter how complex it is from any country because of a standards set of rules, but more importantly an artistic skill for hand drawing skill, flow, symmetry, aspect ratio, size and gaps or fill factor, annotations, labels, values, test points and proper labels.
If you've ever tried to read an old car schematic with few labels and tons of cross wires, you know some bad examples of schematics.
A good schematic has elegance and complexity yet clear illustration of a easy to read logic for analog and/or digital, no matter what language or country the schematic came from. Same holds true for Programming language documentation and Int'l Air Traffic Control lingo. One language and one set of core rules. Of course you might always get a strong accent, same in drawings, but some of the best schematics I have read are like a good book, and many came from Japan.
I was used to large C or D size after I convinced my draftsman in 1975, that E,F and G size just wouldn't fit on my workbench with dozens of pages. So I coached him on high fill factor and smaller font.
I like to think back at who were the best illustrators of "logic diagrams". WHen it came to block diagrams and simple ccts. HP journals were the best, then came EDN magazine Design Hints.
But when it came to complex Analog with discrete parts, Tektronix and HP had the most readable schematic documents for instruments.
What I liked about Tek. was designators were zoned in blocks of 100 so all parts on the board for one zone for one function started at R100, R101... same for C100, L100, CR100 so they could be recognized easily on layout and logic.
There are hundreds of good rules I can think of, but it would be a waste. Just find your own favorite books of schematics.
Often you need a good block diagram which I also created for my complex designs.
Then , we all used to draw schematics on paper napkins in the cafeteria during breaks. ( not mine .. ref EDN)
**broken link removed**
Then trade magazines always had good illustrators for simple circuits, but often left out important details for simplicity and ease of reading.