I depends on how you do your forward an backward movement. There are 1000 ways to skin a cat.
One way would be.
if leftkey()=1
position object 1, newxvalue(object position x(1), object angle y(1)-90, 1), object position y(1), newzvalue(object position z(1), object angle y(1)-90, 1)
endif
if rightkey()=1
position object 1, newxvalue(object position x(1), object angle y(1)+90, 1), object position y(1), newzvalue(object position z(1), object angle y(1)+90, 1)
endif
Another would be.
cx# = object angle x(cam_obj)
cy# = object angle y(cam_obj)
cz# = object angle z(cam_obj)
if leftkey()=1 then xrotate object cam_obj,0 :yrotate object cam_obj,cy#-90 : move object cam_obj,1 : yrotate object cam_obj,cy#: xrotate object cam_obj,cx#
if rightkey()=1 then xrotate object cam_obj,0 :yrotate object cam_obj,cy#-90 : move object cam_obj,-1 : yrotate object cam_obj,cy#: xrotate object cam_obj,cx#