Guiding Bolt

Guiding Bolt is half damage, half an assist, and the assist is often worth more

At the table. Guiding Bolt is a level 1 Cleric spell: an action, 120 feet, a ranged spell attack. A hit deals 4d6 Radiant damage (14 on average), and the next attack roll made against the target before the end of your next turn has Advantage. Each slot level above 1 adds 1d6. It isn't Concentration, so it won't cost you your Bless or Spiritual Weapon.

What changed from 2014. The rules are the same in SRD 5.1 and SRD 5.2.1: 4d6 radiant, Advantage on the next attack, +1d6 per slot level.

How much it gives. With a +5 spell attack, and an ally with +5 attacking next:

The Advantage is worth the most when the ally's hit matters most: the rogue who needs Advantage for Sneak Attack, the paladin about to spend a Smite, or anyone aiming to finish the target.

The choice that matters is turn order. The Advantage goes to the next attack roll against the target, from anyone, including an enemy. So bolt the target when a friend acts right after you, before a monster's minion takes the Advantage with a swing of its own.

The common mistake is firing it at the monster with the highest AC. That's when the bolt is most likely to miss, and when it does, there's no Advantage for anyone. We explain the Advantage maths in full in Advantage and Disadvantage in D&D.

The human angle. Guiding Bolt is a gift spell. The cleric's turn sets up someone else's moment. Dunn, Aknin and Norton found people who spent money on others reported more happiness than those who spent it on themselves. Players who set up a friend's big hit tend to cheer the loudest when the dice land.

Source: Dunn, E. W., Aknin, L. B., & Norton, M. I. (2008). Spending money on others promotes happiness. Science, 319(5870), 1687–1688. doi:10.1126/science.1150952