If you turn the potentiometer up, more LEDs light up and vice versa.

pot_with_leds.ino

// assign names and values
int green1 = 2;
int green2 = 3;
int green3 = 4;
int yellow1 = 5;
int yellow2 = 6;
int yellow3 = 7;
int red1 = 8;
int red2 = 9;
int red3 = 10;

// the setup routine runs once when you press reset:
void setup() {
  // initialize serial communication at 9600 bits per second:
  Serial.begin(9600);
  // initialize the digital pin as an output.
  pinMode(green1, OUTPUT);
  pinMode(green2, OUTPUT); 
  pinMode(green3, OUTPUT); 
  pinMode(yellow1, OUTPUT); 
  pinMode(yellow2, OUTPUT); 
  pinMode(yellow3, OUTPUT); 
  pinMode(red1, OUTPUT); 
  pinMode(red2, OUTPUT); 
  pinMode(red3, OUTPUT); 
}

// the loop routine runs over and over again forever:
void loop() {
  // read the input on analog pin 0:
  int sensorValue = analogRead(A0);
  // print out the value you read:
  Serial.println(sensorValue);
  
  // number of leds according to signal strength (0 - 1024)
  if (sensorValue > 102)    // 1
    digitalWrite(green1, HIGH);
  if (sensorValue > 204)    // 2
    digitalWrite(green2, HIGH);
  if (sensorValue > 306)    // 3
    digitalWrite(green3, HIGH);
  if (sensorValue > 408)    // 4
    digitalWrite(yellow1, HIGH);  
  if (sensorValue > 510)    // 5
    digitalWrite(yellow2, HIGH);
  if (sensorValue > 612)    // 6
    digitalWrite(yellow3, HIGH);
  if (sensorValue > 714)    // 7
    digitalWrite(red1, HIGH);
  if (sensorValue > 816)    // 8
    digitalWrite(red2, HIGH);
  if (sensorValue > 918)    // 9
    digitalWrite(red3, HIGH);

  delay(1);        // delay in between reads for stability
  for (int i = 2; i < 11; i++)
    digitalWrite(i, LOW);
}