Initial Ideas: Train...

Girl alone, travelling home from a party in London from Waterloo Station.
Starts with her leaving a group of friends to walk back to the station. Filmed from all angles as she walks along, closeups of her face, then extreme shots, then shots of her feet walking through puddle etc.
Idea of hand held shots from behind pillars as she walks through a subway -- creates the impression that someone is watching her.
As she enters waterloo, shots are quicker and more juddery, reflects the pandemonium of the station. Close-ups on clock, (time is running out), she then takes out ticket (Close-up) and goes through the machine onto the train around halfway down platform.
Close-up on hands and ipod, diegetic sound of blast of music in her ears, reflects innocence and how she is not fully aware of surrounding.
A buisnessman gets on train and sits opposite, train leaves station.
Mid shot of her from side on listening to ipod and the blackness rushing past outside, (Careful to not film the camera's reflection.)
Train pulls up to next station, buisnessman waits to get off behind her as she remains seated. Camera does 360 degree shot round her head, audience see's girl, then buisnessman, then suddenly a hooded figure in the distance on the train, right at the end of the carriage. Camera now becomes more jolty, editing picks up speed between the two protagonists.
Girl notices man, becoming suspicious, close-ups on eyes and hands fumbling - vulnerability.
She moves through carriage, (range of shots used) extreme - closeup, some panning also. Juddery as train moves.
Hand held shots of him following her, then cuts back to heras she notices he is following.
As the train draws into next station she gets off, however, catching her bag on a chair so that she drops things everywhere. Meanwhile all other passengers have left and are walking out of the station gates. Finally when she steps off the train hurriedly, the train pulls away from station.
Filmed from opposite platform, train leaving, as it moves out of shot, camera spots girl alone then suddenly the figure standing further away down the platform moving towards her.
Then blackout.

Costume: Girl -- Dressy, however messy hair and make-up (esspecially toward the end when she panics and is hurrying down the train.)
Stalker -- Black duffel coat, hood up, black trousers, (important that audience never sees his face.)

Sound: Non Diegetic sound of heartbeat, getting faster towards end. Could even use in credits and start of film at random times to unsettle audience.