(This phrasebook is based on the dialect of Ishigaki, there are dialectal differences between islands)
"j" is pronounced like a "y" in English. Some syllables begin with a "ng", and this may be difficult for some English speakers. The triangular colon indicates a long vowel.
There is a very, very large dictionary you can get at some bookshops, it comes in two volumes, one Yaeyama->Japanese and the other Japanese->Yaeyama. It also includes a brief grammar.