You should leave enough space between pins. Many premade schematic symbols pack the device pins as tightly as possible. While this minimizes the area of a symbol, it also makes the circuit more difficult to read as you have connections converging fr

A Schematic Diagram is intended to be the documentation of a circuit. So I highly recommend including any simple equations that may be used. This includes LED current calculations, filter corner frequencies, etc.

If the circuit yo use is copied from a datasheet, you can put the reference on the schematic so that someone else can check it later.

You should indicate UART direction. Since UART lines are not always clear which way they are flowing, add a little arrow next to each line to show the direction is cecessary.

What you need to remember is that do not pack too much stuff on a page. People may start complaining if your schematic is fourty pages but the alternative is having rats nest of confusing wiring between parts. Break up the schematic into logical block