Q:

Steps to take before trying to implement screen space ambient occlusion

I very recently started learning modern OpenGL.  I have implemented a wavefront file loader and a basic ADS shading model.  At some point I'd like to implement screen space ambient occlusion.  I tried reading on the technique and I understand the concept, but I have trouble understanding the details (i.e. extracting the depth information and reconstructing the positions in space etc.).  
Thus the question is, what techniques should I learn/practice before trying to implement the SSAO? 

A:

Deferred rendering.  90% of what you need to implement SSAO is found in basic deferred rendering algorithms.  That's one reason why SSAO is often used by deferred renderers; it's a natural fit.