Before getting too far into this, is the airplane type certified? Does it have a maintenance manual with rigging instructions? If it is type certified, and does not have rigging instructions (rare, but possible - mine is such), the type certificate data sheet will tell you what the correct flight control deflections are to be. There are a number of safe/standard practices for adjusting turnbuckles (as well as special tools), and cable tension is important, once the rigging is correct.
If the airplane is non certified, the information you seek is a little less certain. Perhaps a type club for that airplane type...
In any case, the answer you seek here could only come with more information on what airplane you're discussing...