Jewelers in Everquest 2 can create many useful items. As there are two earring slots, two ring slots and a necklace slot, all characters need to keep those parts filled in order to boost their character as much as possible. They can also create idols, orbs, symbols, tablets, tomes for secondary and ranged slots and provide enhancements called runes for scout combat arts. They also create the bottles that alchemists use to create potions - an excellent side business, particularly for beginning jewelers looking to make some extra money. It helps to harvest as much of your own resources as possible. If you would rather work on your trades instead of your adventuring classes, it's often possible to make enough money selling lower tier resources to purchase higher tier ones so that you can further boost your jeweler skill.
When crafting lower level jewelry, it's often more cost effective to only create items that boost statistics rather than those that boost resists. Of course, many lower level jewelers will be just leveling using the tradeskill quests, as it's often hard to find buyers for low leveled jewelry on the broker. As a jeweler, you'll need a fairly large supply of raw materials to level up your skill, and it'll likely be somewhere between hard and impossible for you to turn a profit, even while you're doing tradeskill quests. One of the best ways to manage this is to sell off your excess harvested resources to other players, keeping the ones that you actually use.
At the higher end, you'll be taking raid dropped patterns and turning them into various jewelery pieces that will work well for any class of player. High level craftsmen are relatively rare, as most players instead choose to focus on their adventuring. Make sure that your friends know that you're a jeweler, so that they can pick up all of the ingredients that they need for you to produce great items like the aforementioned Runes that boost the abilities of all scout players. If you don't have something to craft but end up getting a rare gem, it's a good idea to hang onto it until you get all the recipes for the tier that it's used for so it doesn't go to waste. Rare items are hard to come by, and usually someone can make use of what you create. Jewelers are less focused on producing "sets" for specific classes than armorers and tailors, although the statistical layouts of most jeweler items will make it so that they only appeal to one or two classes.