For people who aren’t sure what hiragana is, it is the basic Japanese alphabet. It has letters like these: あ、い、う、うえ、お、か、き、く、き、こ、さ、し、す、せ、そ。。。。
I memorized hiragana in a weekend. My teacher wrote them on small cards, and then she told me the pronunciation of them one by one on a Friday, and I wrote the pronunciation on the back. They were small enough that I had a small box I put them in and carried them around in my purse. Whenever I had a chance, like on the train or waiting to go into an office or something, I would pull them out and go over them. When class met on Monday, I had my hiragana memorized. Flash cards are always the best way. Make yourself flash cards with the pronunciation on the back and drill yourself adding a card or two at a time, and then going back to the beginning and saying them all each time.
After that, I could read them, but to reinforce them in my brain, I kept copying thing in hiragana and saying what I copied out loud. I have never forgotten them, and that was many years ago.