The one thing I would like to add is to have someone who is somewhat of a beginner (if possible) test your instructions. Sometimes we think something is clear, and it may be confusing to others.
An extreme example of this is a favorite English lesson I have taught from 5th grade to middle school students. The assignment was writing the instructions for making peanut butter sandwiches. Then I had different students follow the instructions exactly! (I had a copy to make sure they did) They would leave out the simplest thing assuming the person making the sandwich would know what to do. In their case, they left out things like "open the jar of peanut butter" , "use a knife to scoop out and spread the peanut butter on one slice of bread" which, by the way you hope they have been told to take the bread out of the wrapper. In case you haven't guessed, the point of the English lesson was to never assume the reader knows what they are talking about.