easiest way is to pick mining and herbalism (not skinning, cause everyone has it lol), you will sell what you gather/mine for a decent price. I made 140g before lvl 40 without struggling a bit. The single inconvenience is that you can’t track both herbs and nodes at the same time. I use a castsequence macro and press it from time to time.
Also, don’t sell stuff during weekends, everyone plays then and prices tend to drop A LOT.
…happy gold farming?