Being fluent in Dutch is one of the most important things that will help you land a good job in the Flemish region of Belgium. I asked expats in Belgium who have been here for several years what helped them become fluent in Dutch. I myself am nowhere near to becoming fluent, so these tips I need to take to heart.

Here's what I have gathered:
1.) Download the Duolingo app | You can already begin with learning Dutch without even stepping foot in Belgium. This app is great for learning basic words and phrases.
2.) Enrol in Dutch classes | You need a solid foundation. If you can afford it, go for classes offered by local universities, Universitair Talencentrum (UT).
Click here for info about Dutch classes in Belgium
3.) Speak Dutch daily | This tip came up the most. Conversations really boost speaking and listening skills. The hardest part of learning Dutch in Belgium is people replying in English when they hear you have an accent. Don't give up! Continue to speak Dutch, tell people you need to speak the language. Speak Dutch little by little with family, friends, colleagues. Try ordering and paying in restaurants and shops in Dutch. If you live with a native speaker, allocate at least one hour a day where you only speak Dutch with each other.

4. Join language clubs | Nederlands Oefenen is a great site to find activities and clubs in Belgium where you can practice your Dutch. You can also join a volunteer group like Natuurpunt; it can help since you could practice without any pressure.
5. Watch Flemish TV & films | There are a number of TV channels in Dutch that can help you learn the language (één, VTM, Q2, etc.). You can also download the VRT Nu App which lets you stream TV shows and series for free. Most Flemish shows have Dutch subtitles, which are very handy. Local libraries have a vast collection of Flemish films.
6. Go to your local library | The library is a great source for learning Dutch. Besides books, you can also borrow Flemish shows & films. You can also use their computers and take advantage of their Dutch learning softwares and programs. In Antwerp, it costs €9.50/year to be a member of the local library.