first of all you have to know which Arabic you would like to talk ?
do you want to read about culture ,history and religion ? = Modern Standard Arabic
do you want to talk ,have friends or planning to visit a specific country ? = Egypt , Morocco, Jordan etc ?
the best way to start is by learning the alphabets then start listening to songs ( of a dialect or MSA )
- the songs will help your ears to get used and be familiar with the new phonetics and sounds.
then after that start learning the phrase contraction, then start memorizing words.
I recommend also start searching for a language partner , as she will guide you ,support you with many educational materials and will judge them for you,
finally as an Egyptian I would " promote and recommend " my own Egyptian Arabic as it's widely understood by most of Arabic speakers and also a great part of the pop culture is in Egyptian Arabic - I'm not saying the others are bad or won't help you , others are great with greater people" but if i asked a Portuguese speaker which Portuguese should I I learn , his answer will be affected by own country :D
fun fact Arabic uses the same word logic like Portuguese and his cousin "Spanish".
بالتوفيق :]