Stellarium
When planning a night of astrophotography, it is very helpful to have a planetarium software that will show you objects that are in a good position in the sky depending on the time of the night, as well as the time of year. One of my favorite free planetarium software is called Stellarium astronomy software. It is free and available for Windows, Mac and Linux. With advanced equipment setups, it can even control the telescope pointing. You can download it here. Also Stellarium online is great for tracking comets and satellites.
Telescopius
Once you have picked one or more objects that might interest you for a given night, it is important to see if the object is a good match for the equipment that you have. For instance, planets are very small objects and require a long focal length lens or telescope. If your focal length is not long enough, the planets will appear only as very small objects or even just points of light. Or if you want to image a large nebula, you need a short focal length for a wider field of view. The beauty of Telescopius is that it will give you statistics about the coordinates of the object, as well as its rise, set and transit (when it is highest in the sky) times. You simply enter the object information to get relevant details, as well as third party images. It also give you an area in which you can enter the stats of your equipment such as focal length and sensor dimensions. Using these numbers, a frame is projected on an image of the chosen object. You can then see if the object fits nicely in this frame.
AstronomyTools
AstronomyTools has a lot of useful tools. I find the field of view calculator to be very useful. You can utilize this tool to calculate the field of view of your setup.
N.I.N.A. Software
No astrophotography setup would be complete without automation. There are several paid astrophotography software programs that are excellent. Freeware is not always the most useful or feature filled software (you get what you pay for). But N.I.N.A. is very much the exception. Although the learning curve is steep, there are many useful “how-to” videos available on YouTube. N.I.N.A. can automate pretty much the entire image acquisition process. Check out my review of N.I.N.A.