The important thing about the articulation of r is that the tip of the tongue approaches the alveolar area in approximately the way it would for a t or d, but never actually makes contact with any part of the roof of the mouth. You should be able to make a long r sound and feel that no part of the tongue is in contact with the roof of the mouth at any time. (This is, of course, very different from the "r-sounds" of many other languages where some kind of tongue-palate contact is made.) The tongue is in fact usually slightly curled backwards with the tip raised; consonants with this tongue shape are usually called retroflex. The "curling-back" process usually carries the tip of the tongue to a position slightly further back in the mouth than that for alveolar consonants such as t and d, which is why this approximant is called "post- alveolar". A rather different r sound is found at the beginning of a syllable if it is preceded by p, t or k; it is then voiceless and slightly fricative. This pronunciation is found in words such as 'press', 'tress', 'cress