It's a good idea to review mental-math ways to multiply and divide by powers of 10 before teaching students how to compute with decimals or how to write repeating decimals as fractions.
Consider teaching about absolute value before you try to teach students to compute with signed numbers. If students understand the concept of absolute value, they will find it easier to notice patterns in computation with signed numbers and to internalize short cuts for this work.
The rules for subtracting with signed numbers are complicated. Consider emphasizing the inverse relationship between addition and subtraction and encouraging students to rewrite every subtraction exercise involving signed numbers as an addition exercise.
Work with students to create charts for the classroom showing patterns in computing with integers and other signed numbers. The particularly powerful patterns you should emphasize are:
the inverse relationships add/subtract and multiply/divide.
the differences between computing with two numbers whose signs are the same and computing with two numbers whose signs are different.