I have published worksheets on ordering decimals before, but this page, lent to me from urbrainy.com is a very neat way of making sure that decimals are put in order correctly.
It suggests a very simple, step by step, approach which includes:
1. putting the numbers underneath each other, in a table, making sure that the decimals all line up.
2. filling any empty spaces with zeros, making them all the same length, with the same number of digits.
3. beginning to compare, starting with the units column.
Children who have not used decimals may well think that the size of a number depends on the number of digits so comparing decimals can be tricky, as a three digit number such as 0.19 is smaller than a 2-digit number such as 0.2.