To provide useful photometry of your star, you'll need to measure it relative to a star that we are pretty sure is not varying with time.
The easiest way to find comparison stars is through the Variable Star Plotter (VSP) utility provided by the AAVSO. You can search for practically any variable star, and it should call up a chart with comparison stars numbered. If you click on "Photometry Table for this Chart", you'll get V magnitudes and B-V colors for the comparison stars. Recall that our CCD's field of view is ~10 arcmin, so you'll want to ask for something a bit larger than that. If you select "CCD" for "Chart Orientation", the finder chart should be oriented in the same way as the CCD images you observe. A magnitude limit of ~17 should serve you well.
You'll want to select comparison stars that are not near saturation in your images (<40,000 counts at peak). You'll also want to use 2--4 comparison stars, just as a check that no one of the comparison stars is acting funny (i.e., varying) during your observations.