pronouncing TH in THAT, THIEF ,THOOTHPASTE
Yes, this one was a challenge for me too. One time, the teacher sat across me - face to face, she opened her mouth and I was to position my tongue the way she did, and I was repeating the kind of 'hissing" sound after her! :)
She did it to all who had a trouble with the right sound...It was so funny, but it worked!