Believe it or not, many of the areas of the game world are quite civilised. Within these areas, the local police will intervene quickly to stop any fighting, trespass or smuggling.
Thanks to the wonders of modern medicine, death and serious injury are quickly repaired so punishments tend to be light and financial... jail time is rare for most people.
With that in mind,
* Use consider before deciding to give someone a good kicking, to see if you're likely to get in trouble! However, combat outside towns and spacecraft is often unreported.
* Don't try to smuggle drugs, illegally manufactured alcohol or other suspicious materials through customs!
* If you're a civilian, don't try impersonating a member of the armed forces, wave around a weapon in public or smuggle MOD equipment.
There are other things as well, but if you can't work out whether what you're doing is naughty, then you'd best be prepared to pay the fine!
Fines are extracted directly from your bank account.