...start a conversation on a tube.
Tip One: eat a packet of pickled onion monster munch.
I have done this three times now on the Jubilee Line on the way home from work and each time someone (or to be more specific a man) has spoken to me. (Just in case you were wondering I didn't eat them to start a conversation but because I was hungry). I think all three were variations on the "do they still make them?" type comment. The second man was very lucky actually because I gave him a spare bag to share with his friend. Childhood memories flooded back for the pair of them. Who says traveling on the tube is a waste of time?
Tip Two: just start bloody talking if you feel the need
Now, my childhood memories were evoked by a man with a rubic cube on the tube Tuesday night. I had quite a debate with myself as to whether I would talk to him (and also what nationality he was) because he had a too-open shirt which displayed a rather clammy, pasty looking chest with sparse patches of hair which wasn't at all appealing. I took the plunge and asked where he'd picked the cube up from and he chose to ignore me. Bastard.
This tip may be useless as it didn't work in this instance.