Learn hiragana and katakana first! Once you've learned them ONLY read and write in Japanese in kana, otherwise you're holding yourself back!
Also, make sure that you're pronouncing them right... There are plenty of sound files on the internet.
Once you're comfortable with them and have a bit of vocab under your belt, start on the kanji.
I suggest you focus a lot on the grammar first. Once you've learned the basic grammar rules you can start playing with the language, making up stupid sentences and the like... And it's always better to learn by being silly! =D
Learn some of the basic particles asap too! They're awesome!
Personally, I don't suggest getting a textbook! This is my own personal preference, I just find that textbooks hold you back a bit by giving you prescribed amounts of knowledge and by holding your hand far too much. For me, learning Japanese is exciting and vibrant, I don't wanna be held back! Personally, I'd get a good quality Japanese grammar book. You can learn the vocab and kanji you need on the internet very easily (and freely!)... A grammar book will give you guidelines to follow as far as what you should learn next is concerned, without holding you back.
As for vocab, I suggest you start basic; numbers, days of the week, weather, who, what, where, when, why.... Work your way up from there.
Also, stop conning yourself that you're slow at picking up languages or that you're not a language person! It's simply not true and by telling yourself that you're just holding yourself back! You've learned English and the only thing stopping you from learning 20 more languages is your own lack of confidence! Fact!
Websites:
First website I used. Really good for beginners -
http://www.genkienglish.net/genkijapan/menu.htm
Free worksheets from super-basics to advanced stuff -
http://www.mlcjapanese.co.jp/Download.htm
Your new best friend -
http://www.jisho.org/
Amazing Kanji dictionary -
http://www.yamasa.cc/members/ocjs/kanjidic.nsf/SearchKanji3?OpenForm
Those are some of my favourites! But don't be afraid to use google! A lot of people will argue that it's hard to find what you want through google... But I found all of my favourite websites through google!
Good luck! Try your best!! ^-^