One problem a lot of Japanese learners face is the problem known as "being able to do conjugation." To change 行く to its negative form do you say 行くない or 行かない? How do you conjugate 必要 to be past negative polite? Japanese Conjugation Practice let's you drill verbs and adjectives in this way. After spending some time with it, I feel like it could be a good way to improve your ability to conjugate, though I highly recommend taking advantage of the options menu to narrow down the conjugation questions you're being asked.
With prompts like "past negative affirmative," it can be difficult to know what it's asking for at first. But if you tell it to drill you on one or two categories at a time, you'll be able to work deeply into one category and get in more reps. Do you have trouble negating verbs politely (i.e., using ません)? You can focus purely on that until it's simply no longer a problem for you. Then do the next most difficult conjugation for you until you graduate the tool. If you do it this way, you'll be able to spend more time studying and less time trying to parse what it's asking for.