The grammarians tell us that K and Q are always found at the beginning
of a syllable:

[Prisc. Keil. v. III. p. 111.] Q et K semper initio syllabarum
ponuntur.

They say also that the use of Q was more free among the earlier Romans,
who placed it as initial wherever U followed, --as they placed K
wherever A* followed,--but that in the later, established, usage, its
presence was conditioned upon a vowel after the U in the same syllable:

[Donat. Keil. v. IV. p. 442.] Namque illi Q praeponebant quotiens U
sequebatur, ut _quum_; nos vero non possumus Q praeponere nisi ut U
sequatur et post ipsam alia vocalis, ut _quoniam_.

Diomedes says:

[Keil. v. I. p. 425.] Q consonans muta, ex C et U litteris composita,
supervacua, qua utimur quando U et altera vocalis in una syllaba
junguntur, ut _Quirinus_.

R is trilled, as in Italian or French:

[Mar. Vict. Keil. v. VI. p. 32.] Sequetur R, quae, vibratione vocis in
palato linguae fastigio, fragorem tremulis ictibus reddit.

(This proper trilling of the R is most important.)

S seems to have had, almost, if not quite, invariably the sharp sound of