Lately I have heard more than one slightly incorrect way of pronouncing a German T.
For this reason, I feel the necessity to clarify how to do it correctly and to show you how to form a perfect German T:
It all starts with the right position of the tongue .
So, open the lips slightly and keep them relaxed,
the upper and lower teeth being slightly separated.
Rise your tongue so that its tip touches the dental ridge (alveolus) and air pressure builds up behind the tongue.
Do not roll the tongue backwards so that the tip touches the palate!
Do not let it touch the teeth either!
Now, when the tip of the tongue springs down it suddenly releases the air flow with the help of your diaphragm and voila: now you know how to form a perfect German T!
If you want to read more about plosives, you might want to read this blog article on plosives.