This is a good tutorial on both astro photography and doing star trails. Astro photography alone is very technical and I have tried it several times and it’s not easy to get especially if the sky is pretty cloudy. Make sure that your camera settings are correct, using iso3200 or 6400 depending on what you have. Make sure that you are capturing using RAW. 30 seconds of exposure or higher. Set the focus right since it’s not easy to focus on the stars. Make sure that they sky is clear.
My Fujifilm HS25EXR was not good for this, even though it has support for high ISO, apparently it adjusts the exposure time to a faster setting each time I go for a higher ISO. So, results are pretty much the same in terms of light output, but much grainy using a high ISO. So it’s not reliable to take pictures of the stars. While my Pentax has only iso3200 as a maximum, recommended is 6400, but I don’t have much of a choice.
At first you might not see anything properly, but this is where software is important. You need a good RAW editor, so far RawTherapee (it’s free) and Lightroom is very good, of you can use Photoshop. You’ll need to edit it to show more detail on the stars.
Star trails is more of patience, once you already know how to do Asto photography. Doing star trails is pretty much straight forward, but you have to have the time and patience to do it. Make sure that the camera is steady, it must not move from it’s current state, so if your batteries is in a position where you have to remove it from the tripod, that may cause a problem with your shoot. So make sure that you have a fully charged set of batteries before starting it. Once you have set everything, it’s just a matter of repetition. Taking photographs, long dark nights and all.