What is the best way to deal diferent resolutions and gameobject sizes?

Hello,i am new with unity and i am learning every day, i am been reading some tutorials but they only speak about GUI and i have sprites :/

What is the best way to deal diferent resolutions and gameobject sizes?

with the position i have been able to do this

 _Player.transform.position = Camera.main.ScreenToWorldPoint(new Vector3 (Screen.width /6, Screen.height /2.6,10));    

but about his size i am still trying to find out some formula...at this moment i have this

 _Player.transform.localScale = Camera.main.ScreenToWorldPoint(new Vector3 (Screen.width * 0.5, Screen.height * 0.85,10));    

i think i shouldnt use localScale because i have diferent objects with diferent scales... what do you guys suggest? any ideas?