Two different scenarios to write an instructional document would 1- When a consumer is putting say, a dollhouse together and 2- when a friend needs to find the nearest coffee shop. If the instructions are for a consumer, you want to be professional and to the point. If you're texting a friend directions to a coffee shop, you don't need to be professional. The audiences in these situations tell you how the tone should be. If you're writing to a consumer, you need to be professional so they will buy your products again. If you aren't, you may lose profit. If you are writing to a friend, they know you, and understand what you are trying to say.
Thats 7 sentences. figure the rest out lol.
Hope this helped~~