Write down the original decimal. For example, start with .0004.
Count the number of spaces starting at the decimal point to the right and ending where you want to place the decimal point. In this example, count to the tenths space, which is one space from the decimal point.
Multiply by a power of 10 for each space that you count. In this case, multiply .0004 by 10 to get .004, moving the decimal point one space to the right.