I'd recommned Anki for this, there's a lot of hiragana/katakana decks out there. You could even just start learning how to read and write words if you wanted to speed along the process a little. Download a basic words deck for Anki or do the basics in Memrise and read the word, write it down a few times and you'll remember the characters rather quickly. If that sounds too stressful, then limit yourself to 5-10 new characters a day, and every week you'll be learning 35-70 characters! It seems daunting at first, but trust me, it gets a lot easier once you start.
This helped me practice a lot! I learned hiragana in 1 day using this and a normal chart. I'd do the ones I remembered and try learn 1 or 2 and try it again, and repeat. It may be specific for me it working so well but it'd be interesting to see if it helps others.