i learned with flash cards also. after you can identify them really fast, move on to the next set of 5 characters. if you have a hard time, try to associate the characters with something you will remember... such as "mu" looks like a cows face that goes moooo, "ku" is cool because it's easy, blah blah
that's how i learned it. after you learn it randomly lay them down and try to read the fake/real words you just laid out, that will help you read faster too.