What are some things that are good to do in Product Hunt before launching?

Generally, yes, it's important to engage as much as possible to build a community that will support your launch! There is also this checklist you can look into; there are some tips on that too, like finding Slack and Telegram communities where people support each other's launches 👇 hunted.space/guides/product-hunt-guides/how-to-win-on-product-hunt

Having an engaged community is THE best foundation for a successful PH launch. So it is best to start cultivating a community as early as possible. But you can also use any other networks you have: Twitter, Reddit, Newsletter, etc. Without any of those it will get hard unless you have a super viral product.

Before launching on Product Hunt, it's crucial to actively engage with the community by commenting on and upvoting other products to build visibility and connections. Additionally, gather a group of enthusiastic supporters who can help amplify your launch day through social media and direct outreach.

I see that a lot of good advice has already been written, my advice is to make a video for the product.

Yes, community engagement is essential. Connect with makers and influencing people outside of PH like LinkedIn or X.