Try setting it up like the Reference page example
Analog reads are only 10 bits, use int instead of float, value readings will be 0 to 1023 representing 0 to 5V.
Also: It takes about 100 microseconds (0.0001 s) to read an analog input, so the maximum reading rate is about 10,000 times a second.
So your loop is likely going way too fast.
int analogPin = 3; // potentiometer wiper (middle terminal) connected to analog pin 3
// outside leads to ground and +5V
int val = 0; // variable to store the value read
Serial.begin(9600); // setup serial
val = analogRead(analogPin); // read the input pin
Serial.println(val); // debug value