I'm not a fan of doing tons of worksheets, but there are some math skills where my students really need extra practice. We've recently worked on the distributive property, which is really tricky for me. The first year year I taught it, I had to go online and teach myself how to use the distributive property myself! It really surprises me that my students love doing it, and think that it is so easy, but I'm not complaining:)
Here is a worksheet that I've used in my class for extra practice. I've scaffold it, so that it starts of fairly easy and progressively gets more difficult.