The first thing I would say is relax. Don't try to sound like a native speaker.
Why? Well, it is extremely difficult to try to sound like a native speaker of any language. Trying to sound exactly like a native speaker is something that most people will never achieve. Even after years and years of living in another country, the locals know you are a foreigner as soon as you start to speak. Even actors who have spent thousands of dollars on voice and accent training still sound strange to native speakers. Also, there are many different types of English spoken around the world, and someone in another country, or even someone from another part of Britain sounds very different to me. I'm sure the same could be said of Arabic speakers?
What's the answer then?
I think that you (and everybody else learning a language) needs to think about why they want to learn the language. Most people will say they want to be able to communicate. And there is something which does not have strict rules of pronunciation which allows people to do this - International English. My message to non-English speakers is please don't believe you must sound like us. We like the fact that you sound a bit different. The world would be boring if we all sounded the same. You only need to make your pronunciation good enough so that we can understand. That's completely different from sounding like a native speaker.
Watch videos, films, TV, with or without subtitles, listen to the radio, speaking books, talk to other language learners, obviously speaking to a native speaker is often best, but there are millions of speakers of Dutch, German, Brazilian, Chinese, Russian, etc, etc out there who use English everyday. Find someone who will help you correct any mistakes you make. The teachers on here spend most of their time doing this - that is what is so great about Skype, Google Hangouts, etc. If you need specialist help, find a teacher.
And lastly, be patient.