Ok, I'm here again to explain the rules to make plural of words terminating with cia and gia.

First of all, you must control where the stress is.

If the word has the stress on the last syllable, the plural is always -cie or -gie
Otherwise, you must look at the letter before cia or gia.

Is it a vowel? The plural will be -cie or -gie
Is it a consonant? The plural will be -ce or -ge

Examples

mancia/mance (tip i.e. you give the barman when you pay your drink)
lancia/lance (spear/lance)
faccia/facce (face)
forgia/forge (forge)

camicia/camicie (shirt/blouse)
socia/socie (female member of an association)
valigia/valigie (bag)

farmacia/farmacie (the stressing is farmacía, pharmacy)
regia/regie (the stressing is regía, movie direction)

Additional notes

Many times you can find some plural in addition to the original ruled ones:

provincia/province (rule) or provincie (also used) (province)
ciliegia/ciliegie (rule) or ciliege (rarely used) (cherry)
camicia/camicie (rule) or camice (also used¹) (shirt/blouse)
valigia/valigie (rule) or valige (rarely used) (bag)

There are some other terms with double plural, but follow the rule and you'll never get wrong!

^{(1) The plural camíce may be confused with the singular cámice (medical coat), because in written language you don't indicate the stress. So, if you want to write in good italian, never use this form.}