I learned how to write kanji (or got started doing it, at least) by printing out these worksheets made by a WK user, which have the kanji ordered by WK level. Makes it really easy to practice writing kanji that you’ve already learned.
By the time I’d learned how to write a few hundred kanji, stoke order came pretty easily to me, and I can now write most new kanji without having to look up stroke order charts, and am able to draw unknown kanji on the IME pad and get it to give me the kanji that I’m looking for 99% of the time.
Granted, I have not memorized how to write very many kanji, just practiced a bunch, but I’ve gotten loads of additional practice writing the kanji I use in my textbook exercises. An app might be a better choice for testing your long-term memory, but I think those printable worksheets are a great way to learn initially.