Hi

Hey there!
It is safe to go there in the day time, if you are alone, and you are coming out while its still daylight. But its always good to be with mates rather than on your jack jones, especially if you are not familiar with the area... definitely dont get lost.
if you go out at night in lisbon, do it accompanied!!! I recommend being in groups of at least 3 people.
Also, dont go on the tube (metro) alone at night. big chance of getting mugged. I was with a friend, afternoon time and we had to run away from a gang at campo grande metrostation.

Dont flash your mobile phone anywhere. they come in gangs. lol.
maybe its best not to use backpacks or anything good to be snatched. expensive brand clothes and sneakers should also be avoided in the night time hehe.

Im not exagerating

And most importantly dont look like a tourist or an expat hehe!

Valentina