agar agar... you want the water to be circulating well in the tank so that there are no dead spot.
can look up from the under side of the water surface too... make sure there is no oily film stagnant in a corner.
when you do your rock scape, try to have "holes/ caves" for good circulation.
Have minimum rocks in contact with the sand bed.
Make sure rocks are touching the tank base and not just the surface of the sand....
cause if not, later when you siphon the sand, the scape will collapse.
some corals like higher flow and some like lower flow... do take note and position them according to their preference.
some corals are more light demanding and some are not, those that are, place them higher on the rockscape.
Last but not least... time to start your tank thread!