Serial.println(analogRead(A0) / 204.8 ); // should be enough to get the 0-1023 output from A0 read, converted and printed to 0-5volt. Assuming Arduino's 5volt supply is 5.00volt (which is rarely is).
Not sure if OP wants 0.00 to 5.00, or some other made up and/or inaccurate numbers like 0-100.
This sketch prints 0.00 to 5.00 (without using it further).
Leo..
void setup() {
Serial.begin(9600);
}
void loop() {
Serial.println(analogRead(A0) / 204.8);
delay(250); // slows down printing, so humans can read it
}