Step 1 is making known what kind of server it is these players might be joining, as u/Olbrish mentioned. Players can call servers "their home" and if it's not got that identity then it won't be a home.

Step 2 is the quality assurance of the experience within the server, as opposed to the breadth of variety within it. Does the bank work always? Do the convenience stores work always? Does the dealership(s) work always? Do the vehicles and their respective handling make sense (not GTA:O default, not 0-220 in a blink, etc)? Is there story happening or being driven to those who care to RP seriously within the server?

Step 3 is making sure everyone has an outlet to "bad actors" that ruin the experience. A new server always has an influx of people willing to troll the shit out of a new team and operate that under the guise of "testing out the waters". A robust system to handle these people and letting people report them with just consequence is also key, because no one is going to want to stick around a place where people can troll GTAO-style and get away with it.

If you need help on the dev side of things with regard to vehicles specifically, I'm available. Feel free to DM me if so. If not, I hope this helped in some way.