Usually we smile and look straight into the camera because this is what normally leads to the best photos. One trick that can help such photos not to seem staged is to try and think about something really funny and start laughing about it right when someone is taking a photo. This way you can make sure sour smile does not look artificially.
And that`s right, the pictures really do look great then, but from time to time it can get boring to only have this one kind of perspective. This is why occasionally photos on which you do not look into the photographers direction can be very beautiful.
It is also helpful to have your fellow travellers takes pictures simply as you are on the go, walking naturally or admiring some monument. Normally then you do not look at the camera and the pictures are mostly great because they do not seem staged in any way.
You want to take lots of different photos and find the greatest poses for each location? Read Photos - vary your poses!