Let’s have a look at the consonant c. If it precedes –a, -o, -u, it is pronounced [k] as in calme (calm), curiosité (curiosity), cousin (cousin). The only exception is second (second).
Whereas, if it precedes –e, -i, it is pronounced [s] as in ici (here) and ceinture (belt). In order to keep the sound [s] before –a, -o, -u, the consonant c takes the cedilla as in français (French), leçon (lesson), reçu (receipt).
The groups ch and sch are pronounced [ʃ] as in chercher (to search), but in some cases their pronunciation is [k] as in orchestre (orchestra).
Now let’s pass to the consonant g. When it is followed by –a, -o, -u, its pronunciation is [g] as in gourmand (greedy), while g + -e, -i, is pronounced [ʒ] as in sage (wise).
Let’s go on with the group ll. When it is preceded by –i, its pronunciation is [ij], as in fille (girl). The exceptions are ville (city), tranquille (quiet) and mille (a thousand) that keep the sound [il].
The consonant p is silent when it is followed by -t, as in sept (seven), whereas, as in English, the group ph is pronounced [f].
Now let’s have a look at s. In general its pronunciation is [s], but if it is between two vowels or before –b or –v, it is pronounced [z]. Compare: soir (evening) and ruse (cunning).
The last two consonants we will consider are t and x. The pronunciation of t is quite easy, you just have to know that, in some cases, when it is followed by –i its pronunciation is [s], as in émotion (emotion), spatiale (spatial) démocratie (democracy), but you keep the sound [t] in amitié (friendship) and garantie (guarantee). The pronunciation of x is a little more difficult. Generally speaking it is pronounced [ks] as in prétexte (pretext). When it is preceded by –e its pronunciation is [gz] as in exercice (exercise), but sometimes it is pronounced [z] as in dixième (tenth) and sixième (sixth).
Last but not least, remember that the consonants d, p, s, t in word-final position are generally silent: you can easily remember this group of consonants thinking about the word DEPOSIT, that contains them all.