The skill emphasized when learning decimals is place value. Place value is at the essence of understanding the meaning of digits to the right of the decimal point. If you regard the ones' place as a separate entity, then the places to the right of the ones' place mirror the places to the left of it. The places to the LEFT of the ones' place end in "s' (10s, 100s, etc.), while those to the RIGHT of the ones' place end in "ths' (10ths, 100ths, etc.).
While in Los Angeles, I devised a helpful framework that helped students to learn decimals: the "Rainbow Chart." It has a basic symmetry that helps students to understand the relationship of places to the left and right of the ones' place. After students master the Rainbow Chart in its most basic form, I replace some of the decimal values to include decimals and even negative exponents. The MathWise Decimals book includes reproducible pages for extra practice. The "D-Z" (Decimal-Zero) trick reinforces students' understanding of the Rainbow Chart and place value.
To properly understand decimals, students need to get a bigger picture by viewing them in relationship to fractions and percents. An understanding of decimals contributes to students' overall grasp of number sense.