Assuming that we're designing an RPG, I'd keep the side quest challenging to scale with the player's level, I'll make sure to reward players with something they're more likely to appreciate( Like a large amount of XP, cool items, new abilities, ability upgrades, etc.), and I'll make sure that the side quest is not too time-consuming so that the player can return to the main quest without spending too much time on a side quest. I'll also keep the number of side quests in control, to avoid repetitiveness and connect them to NPC from the main quest, to add depth to the game world. Adding a variety of activities( like engaging with various combinations of gameplay mechanics) is also a good thing to keep in mind when designing a side quest.

To ensure side quests enhance the main narrative without overshadowing it, I’d leverage narrative hierarchy and pacing. Side quests should complement the core story, providing depth and character development without diverging from primary themes. Using modular narrative design, I can create side quests that run parallel to the main story, offering lore, character backstory, and world-building, while remaining optional and secondary. Side quests should be triggered by dynamic narrative events, activating when appropriate. Their rewards should offer incremental progression, supporting the player’s journey. Branching dialogue and player choice keep side quests engaging while ensuring they don’t detract from the main storyline’s urgency.