Personally I'd say to level them all up equally, switching off every 5 or 10 levels. The way crafting in this game works, there's a lot of interconnectedness. A level 20 weaver will have recipes that require fibers from level 20 plants, gems from level 20 goldsmiths refine from rocks level 20 miners obtain and leather a level 20 leatherworker can tan from level 20 monsters. If you level gatherers and crafters evenly, you can be self-sufficient. And really, being self-sufficient is the main reason to level a craft.