Whether it be meta tools or apps, or literal concepts like a mineral or a race, for example, a must for me is for the world to be built in a believable manner, and at the most simple, following some decent climate rules without much restraint.
my favourite would be drip plume ice worlds with hotspots that allow for rainforests in 80 Celsius steam zones, very exotic, the temperature regulated by these hotspots.
I rambled on too much…
For me, a map of an area is a must, both from a creator and audience standpoint. My worldbuilding is for DnD, and when I DM it’s very hard for me to start building up cultures, factions, histories etc without having a map of the area first.