A mnemonic is to imagine lowercase d with a bolded curved part and two dots on the vertical part with one dot at each end. The curved part flattens and the vertical part fades as the dot at the top drops down to meet the other dot, forming ▬ ●●.
For the practice:
▬ ●● u c k
▬ ●● ●● l ▬ ●● ▬ ▬ ▬
▬ ●● ● ▬ ▬ ▬ ▬ ▬ ▬ ● ●●● ▬ r ● ▬ ▬ ●
● ▬ ▬ ▬ u ▬ ●● g ●
● ▬ ▬ ● ▬ ▬ ●●
●●●● ●● ▬ ●● ▬ ●● ● ▬ ●