The best method to learn about how radio wave propagation works is to understand the basic principles of ionization and atmospheric impacts on shortwave, mediumwave, and other radio signals. The best article I have found on the subject is called HF Propagation from DeltaDX.com. Study it carefully and review the characteristics not just from the notes but compare with what you hear in your own location and note it during each month. This builds a history that you can refer to for predicting conditions during various times of the year.
Here is a very basic Gray Line map so you can monitor sunrise/sunset around the world to target stations and nations for listening. You can customize this map for your own region at the Earth View Website at this link.
The best page for current propagation conditions is without a doubt from DX.QSL.net.
Also here is a tutorial on Space Weather from John A. Kennewell.
Lastly this is the link to explain the WWV Geophysical Alert Message broadcast each hour at 18 minutes after on 2.5, 5.0, 10, 15, and 20 Mhz.
Current propagation conditions from www.hamqsl.com:
Tables from NOAA explaining the various storm levels and alerts are below. For example a K index of 1-3 is quiet, 4-5 active and so on.