itemize, removing natural indent

emumitem package is a convenient tool. Since version 3.6, it offers a key called "left", with which one can set two tabstops one for the start of label and another for the start of the text. For example in the following MWE:

documentclass{article}
usepackage{enumitem}
setlist[itemize]{align=parleft,left=0pt..1em}
%
begin{document}
%
begin{itemize}
item first item
item second item
end{itemize}
%
end{document}

align=parleft aligns the label to left in the parbox of size labelwidth. left=0pt..1em means that the label (bullet symbol) begins at the margin, and the subsequent text (first item, second item etc.) start at 1em from the margin.

Any customization of a list environment, such as itemize, enumerate, etc, is most elegantly handled by the enumitem package.

You can use leftmargin=* locally,

begin{itemize}[leftmargin=*]
  item one 
  item two
  item three
end{itemize}

or else you use

setlist[itemize]{leftmargin=*}

in your preamble to make the change global.

documentclass{article}
usepackage[showframe=true]{geometry}
usepackage{enumitem}

begin{document}

begin{itemize}
  item one 
  item two
  item three
end{itemize}

begin{itemize}[leftmargin=*]
  item one 
  item two
  item three
end{itemize}
end{document}