Try and aim the air directly into the hole.
For practise, try playing notes that are easy to get a clear sound (i.e E-B ). When you play them, try and relax your mouth (as if you were yawning) and don't use your tongue at all. Take a deep breath (so that your stomach grows) and let the air out in short, sharp bursts. Don't use your tongue- just try and get the sound you want with the air you breathe out. When you are pleased with the sound you have, start tonguing very lightly (use tip of your tongue) at the same time as you breath out in short sharp bursts (like before). With practise, you will be able to get faster, as your stomach will automatically push the air out in sharp bursts.
Hope this helps

(it took me a while, but it worked for me)