Shoot on the wide end of the lens, so you will be able to get longer exposures. At 50mm, shooting towards the eliptic, your slowest shutter speed would be about 4 seconds, before your stars turn into smears due to rotation of the earth. At 8 seconds, you will notice some streaking if you pixel peep.
Therefore, when shooting at the eliptic, (where apparent rotation is fastest) limit yourself to:
2 sec. @100mm
4 sec. @50mm
8 sec @24mm
16 sec @ 12mm
If you are aiming to the north or the deep south, you can double or even triple those times. For example shooting in the direction of Polaris, you can probably get away with a 12 second exposure at 50mm, simply because the star movement is so slow.
If you have access to Photoshop, you will want to process them.
I have found that the best method is to use a high ISO, like 1600 or 3200, and then shoot 8 shots one immediately following another, without moving the tripod.
These shots can be blended together in photoshop easily to average out the noise and to sharpen the details.
Here is a single image, notice the noise! 50mm f/1.8 ISO800 4 seconds. 100%
Now, look at a composite of 8 frames, all blended together in photoshop. 100%
The dimmest stars you see are Apparent Magnitude +8 to +9. Orion is close enough to the elliptic to show trails at anything more than 4 seconds. I could have used higher ISOs, but this was the look I was striving for. Less orange glow in the pictures...
Shooting with higher ISOs and longer shutter speeds will allow hot pixels to show up in your frames. Expect to deal with them, once you have your composite finished. Before they are fixed, your composite will show this...
Nope! That isn't an airplane! You line up the images, by the star positions, and that makes the hotpixels appear to travel across the sky like stars. Cleaning them up at the end is easy.
Also notice some flaring off the brightest stars such as the one around Saiph (bright star at the bottom of the sword of Orion). I was shooting wide open with the lens, which hurts quality in favor of brighter images. The farther from the center of the image you get, the more flare you will notice.