David Chelmick produced a very useful document to identify some of the most confusing Spanish dragonflies, the members of the Darters (Libellulidae).
Those are the most numerous family of dragonflies; many are bright coloured and settle often. For that reason they are easy to photograph and to study.
Download David’s «Spanish Darters identification key» (in english)
Interestingly, the first step in the key is about the colour of the insect (red, black, and so on), so it is quite easy to find out. And the good news is that most of the features are also rather straightforward.
Check his website (again, in english) to find more information on spanish dragonflies.