Board bring-up
there are some general things, like:
1. check if the components are with correct polarity (visual check)
2.check the solderings with a stereo optical microscope (20x-40x magnification), especially on the fine-pitch IC pins. and fix with soldering iron
3. measure short-circuits with a multimeter on all of the power rails. (some cpu cores seem to be short circ, but they are not)
4. connect a lab-power supply with current limit, and measure the current. turn on for a short time and check if the current is normal/abnormal.
5. check crystals and oscillators with a scope. (sine wave should be on crystal pins)
6.check buses with scope, if there is a traffic. especially those buses what are involved in boot.
7. any further depends on your system/board architecture.
go to next step only if theere is no error on the previous step.