Build a small set of phrases you never have to think about.

Fluency feels like automatic sentences, and you can build those one at a time.

A conversation gives you no processing time, so anything you have to construct arrives late. The way through is to have a small number of ready sentences that need no construction at all. Not a long list. Fifteen or twenty phrases that cover the moments you meet every week: greeting a neighbour, ordering, asking for a repeat, buying time to think, closing a conversation, opening a call. When those run by themselves, your attention is free for the part that is actually new.

Choose yours from your own life rather than from anyone's list. Notice the situations where you stall, and write the sentence you wish you had said. Then use it, out loud, until it stops feeling assembled and starts feeling like a single word. That transition usually takes a handful of real uses, not weeks.

Include the small ones people forget: no worries, that would be great, I will think about it and let you know, sorry, I did not catch that. These are the joints of everyday talk, and they carry more conversational weight than any impressive vocabulary. With them running automatically, you sound relaxed. And sounding relaxed makes other people relax, which makes them easier to understand, which makes you more relaxed still.