I am still at the awkward early interaction stage.
How do you know what to say?, usually I can start the conversation but I don’t know where to take it after. How are you able to shift to the next stage when you have both agreed that the weather today is nice.
How do you get over the feeling that you are wasting their time?
Finally, how do you end the conversation when you're still going in the same direction or waiting at the same place?
Honestly, it doesn't really matter what you say. It's mostly about body language and not seeming like a threat (smile). You can talk about whatever. Tell them about a movie you just saw and ask them about recommendations. Ask them for restaurant or dinner suggestions. Tell them about that article you just read which you found intereting.
If they are open to small talk, they will drop some tidbits that you can spring off on. Conversation is a two way street. If they don't seem interested in keeping the conversation going, tell them to have a nice day and carry on with yours.
Those forced conversations have a shelf-life because they’re artificial.
Note, rather, how friends converse and how little scripting is involved. When two good friends meet they don’t say their profession, or academic rank, or ask interrogatory questions. They exchange enthusiasm for each others presence and the conversation tends towards exchanges of perspective/experience and reflection thereof. Statement, vibes, counter-statement(?), more vibes.
That kind of familiar, friendly, approach to conversation is always available and short circuits the scripts. It efficiently probes for people who want to talk and what they want to talk about. It also tends to involve a lot of dumb-yet-charming assertions about the current situation, which takes awareness not planning. A ‘sense’ of humour, not a tight 5 locked and loaded. “Fuck, now that’s a lineup…” isn’t a refined piece of social engineering, but it’s a serviceable conversation starter and the least important part if you’re still talking three hours later.