- Turn too early/late past an arbitrary point in space
- Turn the wrong direction
- Descend too early past an arbitrary point in space
- Use the wrong altimeter setting
- Failing to recognize and troubleshoot a failed instrument
- Failing to recognize signs of hypoxia
Not to mention dealing with emergency procedures while you don't do any of the above
Here is an example from a few years ago where a 777 missed a mountain by a few seconds after some non-standard instructions by ATC