For people I know a little I usually talk about something recent that happened in one of our common areas of interest (e.g. new game releases, what we played recently, what annoyed or hyped me, books we bought and / or read, ...).

Another friend of mine became a parent two years ago and this and the house they are currently building are actually the only things she can talk about anymore, so I adapted and usually start with something one of my niblings did recently (e.g. my 3 year old niece told everyone she can't wait to finally grow up and can do what she wants like going alone to school, eat fries and dance! All very nice life goals IMHO and a good convo starter :D)

For people I know less I try to find something that relates to the current situation (like how I experience things, or what they are currently doing, ...). I feel like it's important, that you are genuine as in you are actually interested in what you are talking about and what the other person has to say.

E.g. after class you can discuss your perception of the lesson (that was loooong / interesting / difficult / ...) and ask them how they perceived it. Or if you meet someone for the first time you can ask how they decided to go to this class and continue from there.

Fun fact: I found my friends at uni (still friends > 10 years later) by befriending the weirdest guy in the group and then being introduced by him. He loved to talk about toilets, maths and how he felt like the Mensa was his new mom. He was super smart and weird and actually everyone liked him because he was honest and real. I used this as a cue to overshare all my weird family stories in that group (not the best conversation starters), I guess the shock value still worked :D

In the end it feels way more difficult, than it is. I still sweat like I've walked a marathon every time. The best tip is that you're genuinely interested in what the other person has to say. If something really doesn't interest you, engage in another topic or ask friendly for more insights, maybe you'll learn something new. Stay friendly and appreciate the time, the person is spending with you and you're good!