The following CNMAT and Wikipedia entries cover all the important explanations of why you need and how to place pull-up or pull-down resistors.
>> http://cnmat.berkeley.edu/recipe/how_and_why_add_pull_and_pull_down_resistors_microcontroller_i_o_
>> http://en.wikipedia.org/wiki/Pull-up_resistor

Analog

For most of our fabric sensors using velostat the internal 20 K Ohm pull-up resistors of the arduino are fine. To set these you’ll have to include the following in the setup function of your Arduino code. The analog inputs 0-5 can be addressed as digital outputs using the numbers 14-19.
digitalWrite(14, HIGH); // set internal pullup resistor for analog pin 0

>> http://arduino.cc/en/Tutorial/AnalogInputPins

Digital

For setting the internal pull-up resistors for digital input pins, the code will look like the following.
digitalWrite(2, HIGH); // turn on internal pullup resistor for digital pin 2

>> http://arduino.cc/en/Tutorial/DigitalPins

The INPUT setting for all digital and analog pins is default, so it does not really need to be specified in the code like this:
pinMode(pin, INPUT); // set pin to input

There are various ways to wire or sew your pull-up resistors.