Keeping in mind that I'm only sharing methods that worked for me, let's take a look at Katakana.
Googling for "katakana" instantly turns up more results that you could ever need. The same 47 important characters in Hiragana have their Katakana counterparts. The image section on google alone turned up 6,500 images for "katakana." You should be pretty well off with one of those charts (^_^).
Of course, using flashcards like the one over at zompist.com is helpful when beginning to drill for katakana.
In fact, I have basically the same advice for learning katakana as I had for learning hiragana.
Some of the pitfalls that you want to be careful of when studying katakana are:
サ (sa) - looks a lot like hiragana せ (se) only backwards.
ヌ (nu) and タ (ta) are one stroke short (or long) of each other. The good news is that not too many words are written with katakana "nu" - words like "new" are written ニュ (nyu).
ケ (ke) and ク (ku) can throw you as well, so make sure you have them straight in your head!
No one I know really likes ソ (so) and ノ (no) and ン (n) - you get used to them after awhile. The best advice I can offer is that you'll probably pick up ン the fastest as you'll use it often. Once you get ン clear, it's easy to differetiate the other two.
The other pairing is ツ (tsu) and シ (shi). Again, focus on ツ because you use it frequently for doubling up the following consonant sound like キッチン (kicchin or kitchen). Once you have the one, the other is easy to remember.
It's 47 characters, and I'm sure you can do it in a day or two if you're really focused. Try some writing exercises. I recommend writing practice books like those on amazon.com