In the majority of cases all quests you're required to consider or take part in are your main Story Quests (MSQ). The MSQ alone almost give you enough XP for you to Lost Ark Gold reach Level 50. or the required level for ending game content. Once you've completed in the Luterra Region and are tasked to travel to other continents, the blue World Quests are your new MSQs.
Outside of the MSQ, you should also always complete Guides Quests. They typically introduce new features to the game, and give rewards tied to those aspects. They're not required immediately, however they are useful items.
The most important items you should get ASAP is the Pet Guide, which gives you a pet rabbit; as well as The Ability Stone Faceting Guide, which will give you a few Ability Stones you can facet to help get Engravings in the future. Pets are great companions who will help you to get your loot, speeding your progress by a lot.
If you're interested in learning more, you can read our in-depth Guide to Engravings in Lost Ark. We dissect what we call the Engravings System and teach you everything you need to learn about it.The majority of Sidequests should be avoided, because they usually only offer little quantities or Silver and Rapport currency. While Rapport currency can be useful later, it's not immediately necessary and there are more efficient options for Rapport items. However, there are some Sidequests that offer excellent rewards, including Engraving Book Chests.
Additionally, there are Chain Quests, which are multi-step Sidequests. In contrast to other Sidequests Chain Quests are almost always worth taking the time to complete. They can also provide rewards that are extremely useful, such as the Engraving Book Chests. You can always come back for these later, much as Sidequests but it's simpler to Cheap Lost Ark Gold complete them when you locate them, meaning it's not necessary to keep track of which ones are available later.