Word-final voiceless fricatives preceded by a voiced sound are voiced before a vowel. That is, AN /f,s,ʃ,x/ become /v,z,ʒ(ɣ)/ between a voiced sound and a word-initial vowel.
/f/ becomes /v/ hoefijzer, vijf uur
/s/ becomes /z/ mensaap, pas op
/ʃ/ becomes /ʒ/ ’n broche op, cash-and-carry
Again, /x/ becoming /ɣ/ will only occur in the South, as in mag ik. Speakers from the East of the country, from Groningen to Limburg, tend to voice all obstruents in this context. For example, /t/ becomes /d/ in kwart over (drie), einduit(slag); /p/ becomes /b/ in (de) trap op; /k/ becomes [g] in (jij) ook al. And for some, it may apply to final clusters like /ts/, as in Limburg Dutch spitsuur, i.e. /ˈspɪdzyr/.
With the notable exception of flapping of ambisyllabic /t/, this kind of assimilation is not common in GA. Remember that in English liaison commonly applies in phrases like this evening, if ever, but that the fricatives remain voiceless. When trying to pronounce these phrases, you may find that you either pronounce them as two words, i.e. with a pause, or with liaison and voicing of the fricative. In practicing these sequences, it may help to pretend that the fricative is initial rather than final, as in /ðɪ ˈsiːvnɪŋ, ɪ ˈfɛvər/.
Within words, AN /s/ frequently alternates with /z/ between voiced sounds, as in consonant, defensie, sensatie. Make sure you pronounce /ns/ in English consonant, defensive, sensation, and /s/ in words like oasis, crisis, basis, freemason.