This is so obvious, but people do it all the time. Most notably, travellers leave their bags at their feet or hanging from the back of chairs when they're at cafes or restaurants. Either keep them on your lap or wrap its strap around your leg.
When moving into your accommodation do not leave bags in your room and your room unguarded/unlocked. Especially helpful to have another person with you, so that one of you stays with the luggage at all times when going into your hotel room.
Photo Gallery Don’T Leave Your Belongings Unattended In Public Spaces
Don’T Leave Your Belongings Unattended In Public Spaces Images
Although maybe you just have too much luggage if you cannot take it all into your room in one go?
I remember one time staying in a hostel in the Middle East for the night, and I was with a friend. We were careful with our luggage. But another man there who was going into the room (it was shared between 4 or 6 people, I forget how many, but it was cheap) left his suitcase unattended and when he came back he could not find it. I had not seen what had happened to it, but probably it was stolen due to neglect.
Hand It Over.
There is a simple rule that people find hard to follow: if you are mugged, give over your wallet, watch, etc. This shouldn't be a problem if you have insurance and you've left all your irreplaceable stuff at home. Just do it, and walk away uninjured.
This is also why it's a good idea to keep money in more than one place, so you hand over the decoy wallet to the mugger with some cash in but you keep another wallet secreted about you with more cash and your cards in.