Tank Placement
things to think about
1) Accessibility: Wherever you place your tank, keep in mind that you will need to be able to access the tank easily and regularly. You will also likely have to hang things off the tank, hang lights over the tank (often from the ceiling), have tubes and pipes running off and to the tank, etc. It's wise to make sure that you can in some way (either by hand or with tongs) reach every inch and corner of the inside of the tank. If you have the room, you will not regret placing your tank such that you can walk (or squeeze your way) around all sides of the tank.
2) Viewability: Aside from wanting to be able to view your tank for pleasure and entertainment, you will need to be able to watch and observe your reef on a daily basis. There is an advantage to being able to see into your tank from as many angles as possible. However, for asthetic or practical reasons, you may have to block view through the back or side panels. That's ok. However, it's wise to leave at least two panels of glass through which you can view the inside of the tank.
3) Electrical Outlets: You will be surprised how many outlets you will end up needing. Just to start, you will need one or two for your lights, one for the protein skimmer, 2 or 3 for power heads and other pumps and one for the heater. That's 5 to 7 outlets just for the basics. Make sure that these outlets are very quickly and easily accessibly.
4) Floods: You can pretty much assume that you will at some point (if not at several points), spill several gallons of water on the floor around the tank. The larger the tank, the larger your spills will be. Most floors in reasonably modern homes and apartments can take a little water. Regardless, you might not want to place your tank on your $30k antique Persian rug unless you're ok with it getting a little wet.
5) Weight: Water is heavy. Some older homes aren't structurally capable of taking the weight of a very large tank. For tanks 50g or less, weight is not usually a concern. However, before planning on a 100+ gallon tank, please consult a surveyor or your landlord as to if your floor is strong enough for such a tank.
Equipment Placement
inside the tank, hang-on-tank, and external
It's a good idea to consider the layout, shape of, and space available in your tank before selecting your equipment. Somewhat contrary to intuition, smaller tanks tend to use more in-tank or hang-on-tank equipment options, while larger tanks tend to use more external equipment options. This is because the external equipment is usually designed to see larger volumes of water and often require an external sump for operation.
Some general tips:
1) Place heaters (and/or chiller coils) in areas of high flow so that heated (or cooled) water is dispersed quickly throughout the tank.
2) Place intakes/feeds away from their corresponding outtakes/overflows. For example, point or place the intake of a canister filter away from the outtake of the same canister filter (this helps make sure that the same filtered water isn't continually going through the same filter).
3) Place your protein skimmer so that it's easily accessible. You'll want to be able to reach and empty the skimmer cup regularly.
4) Experiment with powerhead placement. Figuring out where powerheads (and other sources of water flow) should be placed always requires a bit of trial and error. This may take some time and patience. For more information on water flow, see Water Flow.
5) If necessary, it might be good idea to use extension cords to keep outlets and electrical plugs away from the tank so that they don't get wet.
Accessibility is always preferred. However, space might be limited or aesthetic concerns may motivate you to try and hide certain pieces of equipment. Finding the best compromise between these concerns may take some thought and experimentation. Your local aquarium store and other aquarists might also be able to give you some suggestions and ideas.
Aquascaping
arranging live and base rock
Note: Live rock is just want it sounds like (more or less). It's rock that is taken from the ocean and kept wet when you buy it. It is full of bacteria and other desirable life for your tank. Base rock is usually any rock safe for a reef tank that is not live rock. It's not necessarily rock that serves as a base for anything, it's simply that "base rock" is a more pleasant name than "dead rock."
There aren't too many rules when it comes to aquascaping. Contrary to popular myth, there's no rule about how much live rock or base rock you need. How much rock you should have will depend on your personal preference, what kinds and how much coral you want to keep, what kinds and how many fish you want to keep, the size and shape of your tank, etc. However, there are some things you should think about when purchasing and arranging your base or live rock:
1) Water Flow: placing rock up against the walls of the aquarium tends to limit water flow throughout the tank. Large "walls" and piles of rock also inhibit water flow. However you arrange your rock, try to place it such that water can move around it.
2) Caves: Caves can help with water flow and also give fish and other mobile inverts places to hide and sleep.
3) Live Rock is Better: If there is one "rule" in aquascaping, it's that live rock is better than base rock. Live rock adds to your biological filter. It comes with bacteria and reef critters that add to the ecosystem of your tank. Though live rock is not an absolute must, it's a very good idea. If you have a mix of live rock and base rock, over time, the base rock will eventually become live rock.
3) Too Much Rock: You can have too much rock. Remember that the more rock there is in your tank, the less room and the less water there is in your tank. It's always best to start with less rock (probably no more than 1/6 the volume of your tank) and add more later if you want/need it.
Note: You can measure the approximate volume of a piece (or pieces) of rock by measuring how much water it displaces when submerged. Submerge the rock in water and measure the vertical distance the water rises. Multiply the distance the water rises by the area of the footprint of the tank or container to get the total volume of water displaced by the rock.