Use an ATtiny85 instead of an ATtiny13 - Where do I place the XTAL?
As an electronic circuit designer since my young age on 1972, I would say all logic should ever designed from left to right, all entry points, voltage, signal, etc, should come from left and exit on right.  It is very uncommon to see otherwise, and when it is done, confuse the reader.  If you follow this simple rule, helps a lot.  Also, try to make the circuit as squared as possible, ground on the bottom, voltages on the top, avoid create a havoc of lines, straight and plain connections makes everyone understand immediately the circuit. I/O connectors could either be on the bottom or anywhere in the circuit.