I have not used any BGA packages before, but (lucky for me) my first one is a 0.5mm pitch device.
Since the pitch is so fine, there is no room for vias between the pads, even at the smallest drill size of 0.2mm. For this reason, I have placed the decoupling capacitors on the same side as the BGA, rather than on the opposite side, as is usually recommended. The board thickness is 0.8mm. The passives are all 0201 packages.
I would be grateful if someone experienced with fine pitch BGAs could take a look and see if I have made any obvious mistakes. I have tried to clearly label all of the tracks with their functions, but please let me know if I can annotate the images better.