Had issues learning Dakuten so i found this image online and added the black sidebar as a reminder. Really handy for myself in conjunction with using "Realkana" website. : r/LearnJapanese
漢字練習帳 Genkouyoushi Notebook for Japanese Kanji and Kana Writing Practice, with Furigana, Dakuten, Handakuten Space: Learning Hiragana, Katakana, 120 Pages Tategaki Renshuuchou Book: Designs, Let's Learn: 9798521126941: Amazon.com: Books