While working on Site as site engineer how should be the relationship of workers and Site Engineers/Supervisors for increasing efficiency of manpower?

Relationship should be in such a way that it shall be surrounded with care, mentorship, punctuality, sincerity. In my opinion new relationship needs experience to handle. The time will teach both the parties to cooperate and understand each other. Harsh behaviour often brings discomfort at workplace. For an example if one of your worker is unable to use a tool you can show him in front of others how to operate or use it. This gives  a sense of maturity, understanding, superiority and experience among workers that being a qualified degree holder he (engineer) is able to perform a worker level task although its not necessary for an engineer to perform those task. Trust me this will work.

Last thing.....When we talk about manpower and its efficiency each nationality have there pros and cons. Being an engineer you need to have eagle eye to judge them with respect to skills, quality, work knowledge etc., Once you understand your workers belongs to which nationalities and can do which work efficiently it will be easy for everybody especially you. Things will change gradually. Have trust on yourself. Goodluck !