specific advice is very context dependent but as someone who graduated university very recently and also did what you're planning to do:
- you'll always be nervous whenever you ask out a girl regardless of experience, just accept it as part of life
- if she says no, you'll feel silly for a day or so, but nobodys gonna really care nor remember it as you long as you dont make a big deal about it and you'll also stop caring sooner or later too as life continues
- everytime I was successful, i was always suprised how "easy" it was. It's a very natural thing for a guy to romantically pursue a women, so it's "easy" in the same way eating food or sleeping is because biology does much of the actual heavy lifting.
What that means for you is that you shouldnt focus on trying some pick up line or trying to be overly funny, etc. Just be natural and show some (but not too much) interest in her and that should be enough, as long as she finds you attractive.
- lastly, understand that a lot of it is also out of your control. Either she's also interested in you or she isnt. If she does say no, just make sure to accept it gracefully.
Idk what your situation is (e.g. which country you live in, whether you talked to this girl before etc) but this is how I used to do it, note that I studied in a western european country, non english speaking and I also basically only did cold approach (i.e. I basically never interacted with them before this point):
- since we were in lecture halls, I would always just ask for their instagram/whatsapp so that I could message them later, I didnt ask them out directly because 1. The lecture breaks were quite short and we might need to sort out our schedules and 2. The lecture hall is never really a relaxed environment, so a girl might not be in the mood to say yes to a date at that moment even if she otherwise would - much easier to just get her contact details and then message her later in the evening when she's at her house.
Also, if she says no to giving you her contact details then it's alot easier to walk away gracefully in the sense that there's still a bit of strategic ambiguity if im just asking for her instagram instead of a date outright.
- if i got her contacts then I would msg her later that evening to set up a coffee "date", its not really a real date but just a chance to talk to her 1 on 1 and get to know her, you wanna set up the date in the afternoon/early evening (not late at night because she might be hesistant to go if she doesnt really know you yet)
- if the coffee date goes well then ask her to go on a real one
If you're relatively close to the girl that you're asking out (and already have her phone number/ig etc) then it's probably a better idea to just ask her out on a date directly but still do it in a relatively relaxed environment and not in a lecture hall. (Althouth I dont have any experience with this)
Hope some of this is useful and good luck!