Question about sew in with weave?

well im getting my hair done tommorw with a weave called Harlem 25 and its 100% human hair its italian wet and wavy and im getting a sew in i want it to last as long as possible cause usually when I get a sew in my hair starts to look ugly by the week after..so how do i keep this hair nice for as long as possible.%26amp;%26amp; also do I have to tie it tight at night? cause thats what I did with the other weaves so i dont know..im only 16 by the way