FT makes great points.
One of the only types Day Game I've done / do is on the bus. I think it's a solid two-birds one-stone thing.
A good move to try and start the conversation
at the bus stop and gauge her interest, then sit down with her if she seems interested, which also builds the leading dynamic and compliance. If not, carry on and perhaps open someone who's already on.
As far as when you get on the bus and see a hot girl, I did this at my old school. If it's really crowded, sit very close to them (1-2 seats away). If there's not a whole lot of people on the bus, I would sit directly or almost directly across from her - this will be far more natural for conversation with an empty bus were you to go straight next to her (think of that guy that pisses in the urinal next to you in the bathroom for no reason).
You can open with a simple "Hi (= " or a "How's your day going?" just to gauge interest. I'm sure a specific opener or a compliment could work too, but since you're already there, in a situation together, neither of you guys going anywhere, you don't NEED such an attention grabbing opener to hook her there. She's there, you're there, work a slow build. That said,
if you manage to get her attention before you show that you've seen her, I would try to throw in a contextual opener or compliment to jump straight into conversation as if you've just noticed something in her / about her.
Easy to screen for logistics and adapt your pace too, by asking when she stops. Will this be a 30 second interaction or a 10 minute conversation? Am I gonna have to just shoot my shot and get her number or will I be able to build a good connection / strong attraction?
I've seen a lot of guys trying to hit on girls on the bus before and it be creepy. I think it's important to be warm with low effort and, as FT points out, not overly aggressive or leaving her feeling trapped.
Hue