You should never link sounds in the following occurrences.
#1: Following a punctuation mark.
Voici des étrangers /, un allemand.
Here are some foreigners, a German.
There shouldn’t be a voiced link between étrangers and allemand.
#2: In front of a numeral adjective like un, onze, onzième, huit, huitième (one, eleven, eleventh, eight, eighth).
Vous avez / huit ans.
You are eight years old.
There should be no link between avez and huit.
#3: In front of foreign words starting with the letter “y”.
Les yakuzas
The yakuzas.
There should be no linking sound between les and yakuzas.
#4: Following a word ending with a mute consonant.
Le chat / et le seau.
The cat and the bucket
There should be no link between chat and et le seau because chat ends with a mute consonant (“t”).
#5: In front of a word starting with a h aspiré.*
*: in French, words beginning with a “h” can either be h aspiré or h muet. Both could be roughly translated to “aspirated h” and “mute h”.
Example of words with aspirated h in French:
Hache Hamster Haricot
In the following sentence:
Les haches / coupent les / haricots.
The axes cut the beans.
There would be no linking as both haches and haricots have an aspirated h.