how to start my plot from start of axis

i want my graph to start from start of x axis but also the xticks to be zero at start of x axix and then increase

my code is 

figure(25)
plot((SMed_eq),'-r','Marker','*','LineWidth',1.3);
hold on
plot((SMed_eq_ne),'-g','Marker','*','LineWidth',1.3);
set(gca,'FontSize', 15);
%ylim([200 1200]);
%xlim([0 23]);
set(gca,'XTICK',1:1:24,'XTickLabel',{'0','1','2','3','4','5','6','7','8','9','10','11','12','13','14','15','16','17','18','19','20','21','22','23'});
hold off
h=legend('OBS EQU MED','Ne EQU MED');
%annotation('textbox', [0 0.9 1 0.1],'String','SONM EQUINOX MED(OBS vs NeQuick)','EdgeColor', 'none','HorizontalAlignment', 'center','VerticalAlignment','top','FontWeight','bold','FontSize',12)
annotation('textarrow',[0.075 0.5],[0.6 0.9],'String','Slab Thickness(km)','HeadStyle','none','LineStyle', 'none','FontWeight','bold','FontSize',20, 'TextRotation',90);
annotation('textbox', [0.5 0 0 0.7],'String','LT(hrs)','EdgeColor', 'none','HorizontalAlignment', 'center' ,'VerticalAlignment','bottom','FontWeight','bold','FontSize',20)

Answer 1

[dpb]

But you plotted against ordinal number of observation...

plot((SMed_eq),'-r','Marker','*','LineWidth',1.3);
hold on
plot((SMed_eq_ne),'-g','Marker','*','LineWidth',1.3);

Use

x=0:length(SMed_g)-1;
plot(x,SMed_eq,'-r','Marker','*','LineWidth',1.3);

etc., instead and you can then just set xlim limits to

xlim([0 UP])

where UP is whatever you want for visual effect as the upper x-axis limit. tick labels will match ticks and start at 0 for both with no machinations needed.

As is, you'd need to do something like

hAx=gca;
xtk=hAx.XTick;
hAx.XTickLabel=xtk-1;

but it's simpler to just use the desired x coordinates against which to plot().