- Try to get a as fast as possible testcase that shows this bug; in Arepo: write restart-file right before problem occurs.
- print statements clearly before bug and clearly after
- print statements in middle
- narrow down the location of the bug via bisection
- careful: if you are using queue, make sure to flush standard output since this is usually buffered
- if MPI parallel: figure out which task has problem as soon as possible and just follow this task