Understanding why each step matters
One of the hardest things for students to do is to keep re-writing steps they already know how to do. So often, we get used to doing something, so we shortcut and skip steps, because *we know* what those steps are. But someone else, reading through your page, doesn't understand how you went from point A to point D without seeing point B and C, too. So one of the easiest steps I make my kids (in my classroom, and those I tutor) do is to write down their process - sometimes even making them write it in words.
For example, when working an algebra problem of 3(x-2)=18, I'd make them do all the work:
3*x - 3*2=18, distribution to get rid of the parentheses
+6 to both sides, to get the x term by itself
so 3x = 24
divide both sides by 3, to solve for x instead of 3x
x = 24/3
x = 8
Now, I wouldn't make them write it down with words all the time, but on a test or quiz that might be a 10-point question. And the first few times they learn a new process, I would *definitely* make them do it. Review the above equation. Can you see how much easier it would be to do the next problem, say, 5(x+3)=52, if you had the one above to look at and get the process from? The words help SO MUCH!