Here It's not to hard to find
In summary,
Arduino Serial uses: Data_bits=8, Stop_bits=1, Parity=None, Flow_control=None. This is fixed and you cannot change it when using Serial. Set your PC side accordingly.
Choose a baud rate that is safe from UART buffer overflows and HardwareSerial buffer overflows for your code.
Write short ISRs to prevent UART buffer overflow.
Dangling pins with attached ISR may cause fake and random interrupts that can interfere with system clock and cause UART buffer overlow.
Write loop() carefully to check and read Serial as soon as possible to prevent HardwareSerial buffer overflow.