i can easily open with a girl after eyecontact/smile. just say hi hows it going. but after that i dont really know what to talk to the girl about. i usually have a plan to talk about something but then i run out of things to say.

any tips on this?

I think it is to do with inner game. I mean i have the same problem as you, but Practise makes perfect. The problem with me is not just girls but other people as well. But i found a formula that helps me. Here it is: When you talk about something, after drying that topic out, try to bring up another topic that is somehow related to the previous topic.

Check out the openers section. If you say "hi how's it going," that has many faults. 1. It's boring and you won't have a conversation. 2. She will think you want to get with her. 3. She doesn't want to talk to a stranger and she will be waiting for you to leave.
Use an opener like "hey I've got to get back to my friends soon, but I need a girls opinion on something..." and then you'll be able to talk. Find outlets where you can talk about other things. This gets rid of all your problems.
So really, find a new opener

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-->Turbo<--

a few things:
IT'S NOT A BAD THING IF SHE THINKS YOU WANT HER!!! you will be able to escalate faster

second
for the practice there are hundreds routines like the cube or any other cold reading routines

if i get to a point after opening where it's to early to escalate and we have nothing to say but clearly she's into me I would say something like
StreetLight: "Do you know all those questions like 'where you're from?', 'so, what you do in life etc...', there really random and boring, but it's a stage we have to pass when we meet new ppl"
HB: giggles bla bla bla
StreetLight: "So I have a nicer way to do it.. hmm you look like a student/you don't look like you from around here" (I do it in a joking ridicules tone, and it usually lights the convo a bit)

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second, at some point you don't HAVE to talk you can let her talk, it's BETTER, talking is qualifying, aaaand you can escalate sexually move closer caress her etc. if she's into you she will comply if not.. who cares

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"StreetLight!! Stop seeing every problem in life like it's a chick you didn't hit on!"

Then what are negs and disqualifiers for??
You need to build comfort before attraction. Especially if you're not the most attractive dude out there.

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-->Turbo<--

after some time you realize that you don't have to analyze too much, you can keep a sexual vibe from the start, depending on what you're looking at from the start, you can be super direct but not needy. This whole "OK I opened with 45 degrees and now I need to throw a neg, and now I.. I.. " can really screw up you're mindset, you need to evolve this feeling and you'll just be honest to girls, which means if you think she's cute you'll say it, if you think that "that's not her hair colour but it still looks nice" you'll say it

ps
the fact that youre interested in her doesn't mean she can just HAVE YOU, she still need to work for youre attention

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"StreetLight!! Stop seeing every problem in life like it's a chick you didn't hit on!"

That's very true, but thinking is very necessary for beginners. Yeah they'll fail because of over thinking, but it will become natural soon.

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-->Turbo<--