My answer is about your diagram, not your circuit.
Item 0. The single best thing you can do to get better at this is what you have already done: ask for criticism. This is excellent.
In general, people start by thinking the CAD tool is for telling the PCB what is desired. In fact, it's for communicating with other engineers -- very often your future self -- about what was wanted, what things were for, the intentions.
As such, use everything can you do to make your intention clear. We have special skills at noticing visual patterns, and you can use this to make your diagrams much much clearer.
Please consider the following as well-intentioned general advice.
- The first weakness I see in designers and programmers joining professional groups is they don't use version control either at all, or in a way which works with others. I want to be able to answer, at a glance Exactly what version of what project am I looking at? Yes, even for private projects, yes even for works in progress. Consider something as simple using Status: preliminary and a file timestamp. Once you've filled out the project name on the title block. For real project work, most places I know use GIT, but most places I know have more software engineers than anything else. Your future managers will not let you edit anything at all until they trust you can use the versioning system.
All we see here is an advert for some software.
Give yourself more space. Don't cramp everything up. Consider using a large sheet and then arranging things nicely at a later point. For concrete values, I like to design at A2 which I tidy to A3 once I know where everything goes. And I print reduced at A4 landscape. Consider more than one sheet if that makes things clearer.
If you use labelled signals, you have to look over the whole diagram to find where they go. Use ordinary lines where they make most sense, and use bus connectors to show it's a bus. Consider using "off-sheet" connectors whenever a signal goes out of a boxed area (should each box be its own sheet?). Labelled blocks are good, but use them judiciously. Off-sheet connectors show up well in most CAD systems and indicate "this signal goes far". Usually the signals that leave a section are the inputs and outputs, the purpose, of the section. (Consider this: in FORTRAN and BASIC, we just load up some globals and call some subroutine, and we hope our interim results in TMP don't clash with anything. No programming language since then is designed like that: we always declare inputs and outputs, we always use local variables. Using signal labels as the primary means of connecting signals is just using global variables for everything, and it's as bad in circuit design as in programming.)
Always have higher voltages up, not down. You can solve the ugly tie-to-ground and tie-to-positive overlaps by using off-sheet named signals GND and +3V3 (but still keep symbols for real power supply). If you have a device with multiple power, use the layout to show the multiple voltages.
If you put all the decoupling caps out of the way (in the corner of a box or sheet) it's usually a great decluttering as it moves all the trivial to understand caps out of the way. I like to number the decoupling caps after their chips: U1 gets C101, C102 etc. Number "important functional caps" in main sequence from C1. It also gives the benefit of listing the power needed for a given section.
Don't hide the point of signals. Just because you can connect with a label, don't make the reader hunt for it. For example GPI_X and CSI_X in your level shifter: these are the purpose of this block. Or UART_X.
Always fold signals the same way (/) -- it's very rarely impossible.
Here's a portion of your circuit redrawn with a few of these principles shown.
