For green cards, it's really more about what can you do to increase your chances; for nonimmigrant work visas, the main issues are (these probably aren't non-ob

For green cards, it's really more about what can you do to increase your chances; for nonimmigrant work visas, the main issues are (these probably aren't non-obvious, to answer your question) unauthorized employment, overstay, criminal record, and immigration fraud.