For LRT photo, you may wish to try to take them at about the 2nd
or 3rd floor of some HDB flats in Bukit Panjang or at the platform
itself. MRT you could take at the platform itself too. Maybe you
could tell us what type of scenery or background you would like?
(If you like MRT in the background of some trees or reservoir, you
could head down to Seletar but it may be abit dangerous though. For
BPLRT, there is a stretch of the system where the LRT tracks are on
a hill or something like that where you can take picture of LRT at
the same level of the LRT itself).
However, try to avoid taking photos at City Hall MRT especially
near the control office.