What is the meaning of 豫兮 in 豫兮若冬涉川 ?
You must know that the character 豫  means being caution， being extremely careful;
兮 is modal particle， like 啊.

So,the whole sentence means (他)犹豫小心，就如同冬天过河一样，不敢贸然下水似的. Being extremely caution so that he dare not cross the river in winter.