Don’t study kanji individually. I recommend studying them as they appear in words, although there is a popular book called Remembering the Kanji (RtK) by Heisig which promotes the individual-kanji approach. This seems like a waste of time to me; after spending several months studying RtK, you can’t actually read anything! Additionally, not learning words immediately will slow your understanding of example sentences and therefore grammar.
For my favorite flashcard software, see Spaced repetition and Anki. A popular flashcard deck is the core10k,1 which contains the 10,000 most frequent words in the language. There is a ton of information floating around on how to most effectively use Anki, but the default settings worked fine for me for many years.
Many people recommend making your own Anki deck from new words you see when consuming content in Japanese. I found this to be very time consuming, especially early on when my vocabulary was small, so I preferred using pre-made Anki decks. Now that I have a larger vocabulary, creating my own Anki decks makes more sense.
The core2k/6k/10k decks were removed from the Anki distribution server due to supposed copyright issues, but had been previously released under a permissive license which obviates any potential infringement. At the time of writing, the core10k is available here . ↩︎