Basically, you need about 0.5Vdc to 0.8V dc on the contrast pin (3) of the lcd. You can also get this using a voltage divider consisting of a 10k resistor in series with a 1 k resistor with the 10k connected to Vcc (+5V) and the 1 k connected to ground, and the union of the two resistors (where they connect to each other) tonnected to the lcd contrast pin-3. This will give you the proper contrast to see the text.
It may not be perfect but it will certainly be usable until you can replace it with a pot .