What technique should I use to remove rubble from earth, using a small excavator?
My yard is of similar size, and I had the same problem: rocks, concrete blocks, and trash.  With no previous experience, I rented a Toro Dingo with a few different attachments.


(source: toro.com)  

The attachments I used were:


Soil cultivator.  I used it to till old grass down into the ground, since I was planning to lay new sod.  It tilled grass and weeds far enough into the ground that they did not resurface.



(source: toro.com)  


Leveler.  I used it to, well, level the ground.  As a side effect, it brought rocks and trash to the surface so I could pick it up easily.





Standard bucket for enlarging a large hole (in order to bury concrete blocks), moving large concrete blocks and rocks, filling the hole, and otherwise moving larger amounts of dirt.



(source: toro.com)  

It took me about eight hours for a yard of about the same size as yours.  That included adding 20 cubic yards of new loam on top.  The rental charge was about $400 including delivery and pickup.  It was reasonably easy to make the yard flat, but much harder to make it level because I didn't have any level ground to start from.  If you need your yard to be level, I would recommend hiring someone.