How to pronounce Italian double consonants

In Italian all consonants, with exception of the letter ‘h’, which has no sound, can be doubled.
So in different words of the Italian vocabulary you can have occurrences of bb, cc, dd, gg, pp, tt, ff, ll, mm, nn, rr, ss, vv, zz.
There are no fixed rules to determine whether and when a double consonant is used instead of the single one, and their occurrence needs to be learned as a part of the vocabulary. The letter ‘q’ represents an exception because it is usually doubled as ‘cq’ (as in acqua, water). The word soqquadro (mess) is the only Italian word where a double ‘q’ occurs.
As for pronunciation you can distinguish two major categories. The double consonants BB, CC, DD, GG, PP, CQ, TT are pronounced with a stronger stop in comparison with the words where a single consonant occurs. Take for example the pair Fabio (a male name) and dubbio (doubt), or the pair ape (bee) and tappo (cork).
You can use the examples I have just given to check whether you are pronouncing the difference between single and doubled consonants correctly with a simple exercise. Hold a piece of paper approximately at one centimetre from your mouth when repeating the words. In both cases you should notice that the piece of paper slightly bends when you come to the part of the word that contains the ‘b’ or the ‘p’, however this movement should be considerably more marked if the consonant is doubled.
The second double consonants category includes: FF, LL, MM, NN, RR, SS, VV, ZZ. Take for example the pair polo (pole) and palla (ball), or the pair rosa (rose) and sasso (pebble). In this case the difference between the single and the double consonant is that if the consonant is doubled the sound of the consonant is longer.

Learning how to pronounce double consonants is an important part of learning Italian pronunciation especially because there are many words that differ only with respect to this feature but have completely different meanings. Let me give you an example. The word camino means fireplace, but in Italian you also have cammino, meaning way/road. Here below you can find a list of potentially ambiguous word pairs like this, but the list is not exhaustive. Why not try and find some more? Buon divertimento!

casa house
cassa box, crate
eco echo
ecco here it is
gramo miserable
grammo gram
nono ninth
nonno granfather
pala shovel
palla ball
polo pole
pollo chicken
papa pope
pappa bread soup/food
rosa rose
rossa red
sera evening
serra greenhouse
sete thirst
sette seven
resa surrender
ressa crowd
note notes
notte night
faro lighthouse
farro spelt
sono I am/they are
sonno sleep
feta feta cheese
fetta slice
copia copy
coppia couple
bela it bleats
bella beautiful
cane dog
canne reeds
dona he/she gives
donna woman
velo veil
vello fleece
vile vile
ville villas
seno breast
senno wisdom
bara coffin
barra bar
ano anus
anno year
seta silk
setta sect
fumo smoke
fummo we were
gatò cake
gatto cat
caro dear
carro carriage