Chord numbers in music are usually indicated by Roman numerals.
Here is the 12 Bar Blues progression shown in Roman numerals. The repeat sign C indicates an exact repeat of the previous measure.
Although there are variations from one song to the next, the basic order of chords in a 12 Bar Blues is - Chord I (first four bars), Chord IV (bars 5 and 6), back to Chord I (bars 7 and 8), Chord V (bars 9), Chord IV (bar 10), Chord I (bar 11), and Chord V for the final bar (bar 12).
A good way to memorize a progression is to visualize it bar by bar. Study this blues progression until you have it memorized. Then shut the book and try asking yourself questions like... what chord is in bar 6? (Answer- IV). What chord is in bar 9? (V ), Bar 3? ( I ) etc. until you can answer instantly.