If you want to open direct, say something along the lines of 'Hey I saw you walking past and I thought you looked really cute so I came over to talk to you'. If just want to open without talking just say 'Hey I saw you walking past and I just wanted to say you look really cute'
If you want to open indirect, think of anything situational. I opened four girls today in this manner and will give you examples:
Spotted a girl I recognised from one of my classes: "Hey, you're in my Mandarin class"
Sitting in the bus next to a girl, and a guy gets in at a stop in the middle of nowhere:
"There's nothing over here, is there?"
Waiting for the bus, a blonde girl's friends leave.
"Are you taking the bus to x as well?"
You'll be surprised how easy complete strangers are to talk to if you just say anything. Anything at all. You have to say something after she responds to subcommunicate you want to keep the conversation going, but if you do it'll most likely run smoothly.
If you're just opening for the sake of grabbing your balls and going for it, direct openers will take bigger ones but the reward in terms of practise and growing confidence will be greater. There's no shame in not doing so if it makes you uncomfortable. In that case, just practise finding situational openers.