You can reach a new level by getting XPs. To earn XP you can do many different game actions, such as completing your quests, planting and harvesting crops and trees, decorating your settlement and clearing it from the stones/trees/grass.
     
If you do not have new quests show up, it means that you already completed all the quests required for this level, and now you can focus on replenishing your supplies and decorating your village.
With love,
Your Farland Team