Some people respond well to theoretical arguments. Others definitely do not. Actual ancaps (as rare as they are these days) are the types that will respond well to the former.

Unless you're dealing with a Sanders stan, never focus on completely rewriting the system. Avoid revolutionary terms at all cost, especially for anyone older than like 30ish, as they'll want to avoid disrupting what little stability they've already achieved.

Most of the main ideas of a socialist economy can be accomplished with seemingly minor classification changes (with obviously huge implications). You can present this framework as a series of "shortest-path" alterations from a hypothetical standpoint. You'll inevitably get the "well how do we actually get there?", and that's when you give the "well there's a lot of different thoughts on that, none of which are easy." You can gain quite a lot from presenting big theoretical changes as humble changes presented humbly.

With most people, you should definitely focus on listening to their issues and agitation.

Don’t argue with people about history.

Agreed. Avoid history unless someone directly throws it upon you. It's too much work for not enough benefit. But you cannot always avoid it.

I like to respond to "but Stalin!!1" by painting Stalin as being (correctly) paranoid about their new, fragile system from being destroyed from both powerful people inside and much more potent exterior powers. Say the U.S. was a huge threat because they wanted to capitalize on their people, and without the largest institutional threat (the U.S.), Stalin wouldn't have been so paranoid.

It fits with my response to "socialism has never worked". I say "the United States is the only place that socialism can work because there is no United States to destroy or invade it"...Not 100% true, but it allows you to brush off a lot of propaganda baggage as aggressive U.S. foreign policy and it's role & effects. Also "China adopted a weird variant of capitalism so that the United States wouldn't focus on destroying it."

Ask them about their lives, find the things that are fucked in their life and relate it to how the rich are stealing from them. Don’t try to sell them communism itself as you’ll hit a brick wall, agitate around the exploitation in their lives, find things to empaphise with them on, find the broken things in their world and agree with them how messed up those things are. Relate those broken things to the enemy.

Be very careful with this. Nothing will hurt your efforts more than misrepresenting their work or their problems and trying to commandeer their legitimate issues for political gain. You really should make sure you have a grasp of what their problems actually are before you go about suggesting solutions. Listen closely, especially at first. This is great advice for those you work alongside or those whose work you have intimate knowledge of. Less so for people where you have a decent chance at offending via having ulterior motives about their closely held struggles. This advice is best for building issue-oriented organization vs radicalization.