Hey :)
i've done this before.
you have kind of gotta respect their privacy and stuff so it is difficult.
remember that after a day of working, they are gonna be worn out and people screaming at them isnt gonna make them feel any better.
i suggest waiting near the place they are going to leave,and as they are leaving or when you see them, say politely, 'please could i have a photo?' - they will most probably say yes unless they've had a really bad day. then talk to them about how far you've travelled, then say thanks and go. remember they get this a lot and don't wanna talk for ages.

hope this helps,
xx

Hi!
I wanna go to Prague on set of Child 44 (if someone want to go there, please let me know, together will be better :))
and it's my first time. I want to meet Tom Hardy and Gary Oldman there, take a photo and come back to home. But I have no idea what I have to do to take this photo. They will be in Prague's metro, 10pm-8am so they will be so tired after work, what, how and when is the best moment to come to actors and please about autograph and photos. Maybe someone was on set/backstage and know what I should do to have a succes :) it's really important to me, I intend to ride 166 miles from another country just to met Tom Hardy ;D I renew my question: if someone want to go on set of Child 44 let me know! It will works, I know it!