Writing is essential. I use a few sets of flash cards (daily, weekly, monthly, "right now"), take the top three from "right now", and use some or all of them in a sentence. Then I put them in one of the sets based on how well I know it, or if I wasn't able to write it without help at all I put it back into the "now" set. It works well for me, and in fact I'm out of "daily" kanji... haven't had a chance to add more yet.