Source: http://askubuntu.com/questions/305767/how-i-can-create-shortcut-for-maximize-minimize-window-in-lubuntu?answertab=active#tab-top

Custom keyboard shortcuts in lubuntu

<!-- Keybindings for window tiling -->

    <keybind key="C-W-Up">        # FullScreen
      <action name="Maximize"/>
    </keybind>
    <keybind key="C-W-Down">        # MiddleScreen
      <action name="UnmaximizeFull"/>
      <action name="MoveResizeTo"><x>center</x><y>center</y><width>50%</width><height>50%</height></action>
    </keybind>

    <keybind key="C-W-Left">        # HalfLeftScreen
      <action name="UnmaximizeFull"/>
      <action name="MoveResizeTo"><x>0</x><y>0</y><height>100%</height><width>50%</width></action>
    </keybind>
    <keybind key="C-W-Right">        # HalfRightScreen
      <action name="UnmaximizeFull"/>
      <action name="MoveResizeTo"><x>-0</x><y>0</y><height>100%</height><width>50%</width></action>
    </keybind>

    <keybind key="C-W-1">        # UpperQuarterLeft
      <action name="UnmaximizeFull"/>
      <action name="MoveResizeTo"><x>0</x><y>0</y><height>50%</height><width>50%</width></action>
    </keybind>

    <keybind key="C-W-2">        # LowerQuarterLeft
      <action name="UnmaximizeFull"/>
      <action name="MoveResizeTo"><x>0</x><y>-0</y><height>50%</height><width>50%</width></action>
    </keybind>

    <keybind key="C-W-3">        # LowerQuarterRight
      <action name="UnmaximizeFull"/>
      <action name="MoveResizeTo"><x>-0</x><y>-0</y><height>50%</height><width>50%</width></action>
    </keybind>

    <keybind key="C-W-4">        # UpperQuarterRight
      <action name="UnmaximizeFull"/>
      <action name="MoveResizeTo"><x>-0</x><y>0</y><height>50%</height><width>50%</width></action>
    </keybind>