Well, generally selling runs in a dungeon to help someone else level is a good way to start.
Or get loot charms and run in a place with rings or necklaces.
After you have gold, you can use it to make more money, by crafting, gambling, or buying low and selling high.
Though I think if you are in a tight spot for gold, one of the best ways to get a little money fast is to sell charms you get from the loyalty shop. Usually you get about 100g or so for 19 loyalty shop coins. Sometimes it's higher.
The higher level charms aren't worth getting since you get less gold for the loyalty coins you spend.
On that note, getting war stones and turning them to eden crystals can be a good way to get money, especially if you are in a guild which does territory wars and wins a lot.