Number one rule in reefkeeping: water parameters.
Number two rule in reef keeping: NO IMPULSE BUYING

Research the coral before you buy it to make sure you can meet its needs,and to make sure it is compatible with other coral in your system.
Number three rule in reefkeeping: Never listen to Sponge Bob
Those individuals have done their home work before hand.
They know exactly what species get along, and what species need space.
Finding out which corals sting and which do not is only half the battle.
You must also keep growth rates,and growth patterns in mind.
Some corals will grow much faster than others, as well as spread out and shade or smother near by coral as they grow.
All coral requre initial growing space when you fisrt add them to your
Aquascape.
After you have picked out which coral types you would like to keep you must research them.
Examples of questions to ask yourself before buying a given coral:
Grow rates: will they grow over my other coral and smother them as they grow? Will they over shadow my coral and starve them of light as they grow up and out?.
Stinging capabilities: Does this coral produce sweepers? Will it sting another coral if it touches it?.
"Chemical compatibitly": Will they engauge in a silent and invisible chemical warfare if place down current of eachother or to close to one another?.
Lighting requirements: Since this coral requires (x) amount lighting how will this effect other coral in my tank?
Feeding requirements/dosing: Since this particular coral requires (x) amount of ( a given dosed chemical) to remain healthy how will other corals in my tank react to it? Since this coral requires (any given food stuff) can other corals in my system take atvantage of it as well?
The intitial planning stage is the most critical, and the hardest part (IMHO) in reef keeping.
Once you have researced the coral you would like to keep the rest falls into place.
Those folks who have the "bonzai reef" look that your seeing have researched thier coral for compatibility,and all other needs, as well as trim/frag them regularly as needed.
I hope this helps you out a little more.
