At the Mercy of Strangers is a Secondary quest in The Witcher 3. In it, you get a chance to save a Temerian deserter from certain death. Guide contains image walkthrough and starting NPC location.

Highway Robbery is a secondary quest available in Velen, near the Boatmakers’ Hut.

Bitter Harvest is a Secondary quest in The Witcher 3. In it, you’ll protect a group of scavengers from undead monsters. It is also part of a group of quests that will grant you access to Redanian territory. Everything starts with “Thou shalt not pass” and continues with “Fake Papers” quests. Guide contains image walkthrough and starting NPC location.

A Frying Pan, Spick and Span secondary quest will have you searching for an old woman’s lost frying pan.

Faithful Friend is a secondary quest in White Orchard, available only during the epilogue of the Main Quest: Something Ends, Something Begins (II).

Deadly Crossing is a secondary quest that is available as you explore Velen and Novigrad during Act I.

Defender of the Faith is a secondary quest in the Witcher 3 that is available as you explore Velen.
Guide contains image walkthrough and starting NPC location.

Face Me if You Dare! is a secondary quest that is available in Velen. You will find yourself the unwilling recipient of a challenge from a delusional man. Guide contains image walkthrough and starting NPC location.

Nilfgaardian Lessons – Witcher 3 quest.

Missing in action is a Secondary Quest that is available in White Orchard via a Notice Board. You can help a soldier find the corpse of his brother who was killed in a recent battle. Guide contains image walkthrough and starting NPC location.

Twisted Firestarter is one of the first Side Quests in the game. Blacksmith Willis’ forge has been burned down and you have to find the culprit. Guide contains image walkthrough and starting NPC location.

Imperial Edict Number 18/45 – Witcher 3 quest.

Looking to Borrow a Plough – Witcher 3 quest.

Death to the Invaders! – Witcher 3 quest.

Contract: Devil by the Well is the first Witcher Contract quest you’ll come across in the game. You will have to dispose of a Noonwraith and a nearby Abandoned village. Quest requires some investigation and you have several choice to make. Guide contains image walkthrough and starting NPC location.

Brother Missing is a White Orchard Notice board "side quest" that actually starts the quest Missing in Action (click on this link to see the full screenshot walkthrough)

Gwent: Velen Players – Witcher 3 quest.

Races: Crow’s Perch – Witcher 3 quest.

Fists of Fury: Velen – Witcher 3 quest.

Funeral Pyres is a secondary quest that involves burning the corpses of fallen soldiers. It starts in Velen a bit west of the village of Mulbrydale. Guide contains image walkthrough and starting NPC location.