One way is to focus on doing side quests. They often give a good amount of XP. Also, exploring new areas and finding hidden locations can net you some XP as well. Just be careful not to take on enemies that are too tough for you at the start.
You can level up fast by completing all the assigned tasks and challenges. Also, interacting frequently with other characters and joining clubs can help.
We were unable to find a specific method to level up A Dream to Level 71. The search results mentioned some strategies and techniques for leveling up in the Legendary World and A Dream of the Underworld, but there was no mention of the specific method to level up in A Dream of the Underworld. Therefore, we are unable to give an accurate answer.
Do a lot of missions. The story missions usually give a good amount of XP. Also, participate in races. Even if you don't win, you still get some XP for taking part.
One way is to complete quests regularly. The more quests you do, especially the ones with higher difficulty levels, the more experience points you'll get. Also, try to battle stronger monsters as they give more exp when defeated.
After reaching level 10, Xuanyuan Ce's leveling method was to use the Xuanyuan spiritual contract and the return mystic talisman to level up. The Xuanyuan Spirit Contract could be obtained through the T-series dungeon or exchanged at the Heyang NPC Wei Xiaokan. According to the experience in document [3], if he wanted to level up every Xuanyuan Ce, he would need to prepare at least 50 hands of Returning Profound Talismans. Therefore, to upgrade Xuanyuan Ce to level 10 and above, he needed to prepare enough Xuanyuan spiritual contracts and returning mystic talismans.
Do the theme dungeon quests. They are designed to give good experience for your level. For example, the Ellinel Fairy Academy dungeon has quests that can quickly boost your level.