Articulation points of the and the

The letter

This letter is articulated from the tip of the tongue and what lies opposite to it from the gum of the two front top incisors. is articulated a bit forward on the gums from the place of the .
This letter is not always pronounced clearly, and the articulation point is only applied when it is pronounced clearly, namely when it has a vowel on it, or if it has a sukoon on it and is followed by one of the following six letters:

The rules for the when it has no vowel (saakinah), and is not followed by one of the above six letters, will be explained later, insha’ Allah.

https://www.youtube.com/watch?v=PtsdUGsyWpc&list=PLaZWY4xgUE5WykCSI2ZhwCTUPQ5727SC8&index=22

Common mistakes in this letter

The mistakes with this letter tend to be few.  The most common mistake is that of using too large an area of the tongue and including the top of the tongue, instead of just the tip. 

The letter

This letter is emitted from the tip of the tongue with the top of the tip and what lies opposite to it of the gums of the two front top incisors.  The tip with the top of the tip need to strike the gums to produce this sound correctly.  There should be no trilling of the tongue when pronouncing this letter.

https://www.youtube.com/watch?v=fnCmBwKVMcE&list=PLaZWY4xgUE5WykCSI2ZhwCTUPQ5727SC8&index=10

Common mistakes in this letter

The first and most common mistake in the  is not striking the tip with the top of the tip to the gums.  The English “r” is articulated without the tongue striking on any part of the mouth, so many native English speakers have to practice a bit to say the correctly.  One should physically feel the tongue hit the gum of the two top front incisors. 

Another mistake that some have is using the soft tissue behind the gum for a striking place for the tongue.  It is quite difficult to get the tip and the top involved when the soft tissue area is used, so the resultant sound is deep and rolling, but not correct. 

Still other make the aforementioned error of repeated trilling of the tongue when pronouncing the .  The scholars have cautioned against this.  This usually can be fixed by leaving a small space for the sound to run out at the very tip of the tongue.  If the tip is up tight against the gum, there is no place for the sound to run, pressure builds up and can only released by the incorrect excessive trilling.