with katakana and hiragana, I recommend practicing them a lot, just like Jimmy-san said.
I personally learned them (as in memorized them without any paterns or other stuff to remember them logically) in a single day, but after that, for about 2-3 months I repeated the process of writing and rewriting them in a notebook and trying to remember them by stroke order. I did this almost every day in which I had about 15-30 minutes of free time.
With Kanji, it's a whole new level of trying to learn them. For that, I recommend sticking to the course as Premium Plus and Platinum levels teach you some of them. As auxiliary learning tools (which proved to be quite effective for me) try the first 2 volumes of "Remembering the Kanji" by James W. Heisig. Though this is a very tricky part of learning Japanese and may take you a few years to master them.
Anyway, the main point is: practice a lot by memorizing their stroke orders and by writing them a couple of times/day in a notebook or on a piece of paper.