Here is a list of commands I found useful while making DataPacks :

initialise scoreboards :-
scoreboard objectives add <score> minecraft.custom:minecraft.jump
scoreboard objectives add <score> minecraft.custom:minecraft.sneak_time

reset scores
scoreboard players set @a[​scores={<score>=1..}] <score> 0

nbt of an item
@e[​type=item,nbt={Item:{id:"<item>"}}]

player holding and right clicking with an item
execute as @a[​nbt={SelectedItem:{id:"<item>",tag:{<tag>:1b}}},scores={<right_click_score>=1..}] at @s run

kill entity if its not near another entity [​kills entity with <tag_1>]
execute as @e[​tag=<tag_1>,type=armor_stand] at @s unless entity @e[​type=wolf,tag=<tag_2>,distance=0..1] run kill @s

Passenger tag [​entity 2 will ride entity 1]
summon <entity_1> ~ ~ ~ {Tags:["<your_tag>"],CustomName:'{"text":"<custom_name>"}',Passengers:[{id:"<entity_2>",Silent:1b,Small:1b,Invisible:1b,NoBasePlate:1b,Tags:["<tag_1>"],DisabledSlots:4144959,ArmorItems:[{},{},{},{id:"minecraft:diamond_pickaxe",Count:1b,tag:{Unbreakable:1b,CustomModelData:1}}]}]}

replace players head slot with item
item replace entity @s armor.head with <item>

Some good generators:-

https://mcstacker.net/

https://crafting.thedestruc7i0n.ca/

https://haselkern.com/Minecraft-ArmorStand/

https://vberlier.github.io/animated-models/

I will try to update this post will more commands and tutorials in the future.

If you have any more commands you would like to be mentioned leave them in the comments