Procure a table such as those found in the references. The best of these charts for Americans will present you with each character or letter as it appears in Roman script. This is what you are most familiar with. Then, the chart will show you the letter as it appears in Old German or Sütterlin.
Get some ruled paper and carefully practice each letter in its lower case and upper case form. You will need to do this many, many times to gain proficiency and memory for the letters so be persistent and don't get frustrated.
Do not use umlauted vowels. If you are familiar with contemporary German writing, then you are aware that many vowel sounds are created through the use of an umlaut -- a two-dotted mark that appears above the vowel. Sütterlin does not use the umlaut but instead spells out the two-letter value such as 'oe', 'ae' or 'ue'.
Recognize that the letter 'S' has two values-- one that serves when it starts or comes in the middle of a word and another when it comes at the end. The former, or long 'S,' appears almost as an exaggerated number one while the second, or round 'S,' is close in appearance to the number six.
Make the necessary distinction between the letters 'N', 'U' and 'E'. 'N' and 'E' each have an end hook yet they connect very differently. The 'E' bridges across from the top whereas the 'N', much like the contemporary English 'N,' starts at the bottom and comes up. 'U' and 'N' look very similar. But the 'U' will have a wavy line above it. In order to make the 'N' a double 'N' (as in Anna), place a bar line above the single character.