1) Writing short texts and posting them here is a great place to start! The community is quite helpful and you will get corrections of what you have written. I will be nice of you to help people studying Arabic in the same way when you have time.
2) Pick any songs and movies in English you like, watch them and listen to them. This really helps to improve your listening skills. The most important thing here is to find something you really enjoy but which also suits your level, and again the community here will be glad to answer your questions (like "Will you please recommend some rock/rap/pop/alternative music with lyrics suitable for beginners"). My first recommendation is Beatles with easy songs like "All together now". Pretty much everyone likes them, they are funny and their English is not too complicated.
3) If you like reading, reading books in English will also boost your vocabulary in no time. Just make sure, once again, that it is something you enjoy and at the same time easy enough for you. It may help to read a book that you already read and liked in translation.
4) Do language exchange! Honestly, it's amazing. And you will most likely find a language partner soon because quite a few people are doing Arabic.
5) You will have to do some grammar as well. This is more easily done with a teacher but you can manage on yourself too. Just make sure you are using a good textbook with answers, but don't peek at the answers until you've finished the exsercises!
This pretty much covers the main aspects of any language: grammar, reading, writing and conversation practice. At a language department at a university, these all will be different subjects but you can study systematically yourself as well. Unfortunately, this leaves out phonetics (pronunciation), however, your pronunciation will benefit greatly from speaking with a native speaker and listening to music/watching movies as well.