In Ljub. head for the bus station, which is beside the train station, can't miss it.
BUT, please note that the bus to Bled comes in to it's stop in the middle of the open station (unmarked, without any specific covered/shed bus stop, and if there aren't enough passengers for the scheduled time-slot, they take off!
As for getting off, 'Mlino' is a popular hostel by the Lake, making for a great walk along the lake. 'Grad' is the centre, near the castle-end (though you have to climb up the hill to visit the castle). I suggest picking the latter.
Also, try to squeeze in a bus trip to Bohinj, approx 1 hour away, and well worth it.
Bled is very pretty, you're bound to have fun :) And Bohinj offers some adventurous treks...
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