Write each letter at least 10 times. Your Japanese textbook should show you the stroke order for each letter, but you can also find this online. Writing can help you learn the shape of the letter.
Divide the katakana into sections to study. It's easy to simply use each line of the katakana chart, such as "a, i, u, e and o" and "ka, ki, ku, ke and ko."
Use flash cards to drill yourself on the letters. On one side, you should have the katakana letter and on the other, the Roman letters of the sound.
Write words in katakana. Challenge yourself to combine the letters to make words. Start with your name, then try other foreign loan words. Remember that Japanese "letters" don't end with a consonant, except for "N." This can make the words seem a little awkward. For example, escalator in Japanese is "esukaretaa."
Increase your recognition speed with computer games. Learning doesn't have to be all about flash cards. For example, you could play a computer game where you must quickly type the English way to write the katakana that you see.