Salvete,
I’m using the classical pronounciation and I can’t figure how to pronounce neither vu nor ji, like in ablativus, vulgus, adjiciat, objicit. 
If anyone could describe it to me or compare with anything, will help me immensely. 
gratus.
At the risk of starting some dreadful war over the niceties of pronunciation, I would say (and assuming you can follow my English words):
vu (or, often now, uu) = approximately as in “wood” or “wool”: So “ab la tee wuss”, “wool guss”.
ji (or, generally now, ii) = “yi”, and in “ying”: ad yik ee at.
Basically, v = consonant u = w. j = consonant i = y. Probably not perfect, but “good enough”.
That’s definitely the right method, Ulpiane (nomen mihi placet, obiter).
I’d like to emphasize, however, the pronunciation of the vowels, that is their quality: ‘u’ always as in “opera buffa,” ‘i’ as in “machine.”