To learn Arabic for the first time, I recommend the following steps:

STEP ONE: Alphabet
Work through the following fantastic book slowly and thoroughly:
The Arabic Alphabet: How to Read and Write It by N. Awde and P. Samano
Then do the whole book again.
By now you have a vocabulary of 100+ words, and you know how to transliterate anything.

STEP TWO: Intermediate
To increase vocabulary and learn proper pronunciation, I met with a native Arabic speaker for study (roughly two hours per week for twenty weeks.)  With his guidance, I started to read short paragraphs in Arabic. 

I also did some exercises in Alif Baa by K. Brustad et al (book with audio CD, writing exercises, and listening exercises.) I didn't find this book very useful, but it's better than nothing.

For the next year-and-a-half, I didn't study any Arabic, but I hoped for an opportunity to visit the Middle East.

STEP THREE: Immersion
I attended an Arabic language immersion program in the Middle East. After one month of studying Arabic in Yemen, I could write short essays and hold simple conversations with native speakers.

STEP FOUR: Keeping it going
To learn some more grammar, I plan to study Standard Arabic: An Elementary-Intermediate Course by E. Schulz et al.

In addition, I intend to find opportunities to practice conversing with native speakers. It may also be helpful play the Alif Baa CD, or Arab music in the background at home while doing other things so I can keep learning.

I'll try to read some children's stories online at the International Children's Digital Library.

And of course, I hope to return to the Middle East.