Purchase and set up all non-living components first. The tank, pumps, and heater all need to be functioning (and not leaking anywhere). The lighting should be positioned, and on a timer.
Once your tank is set up and running and nothing is broken, it is time to add the live rock. Live rock can be purchased online or at a local fish store. There may be some die-off; this is natural.
Once the live rock is in your tank, let the tank run for a few days and then test the water using the test kit. Ammonia, nitrites and nitrates will read high at first, the goal is to read zero.
Change the water at least once a week during the curing process. Curing is building a base of beneficial bacteria that breaks down ammonia to nitrite to nitrate to harmless nitrogen.
When changing water, remember to mix the salt thoroughly outside of the tank; never try to mix salt with water in the tank. Also, when water evaporates remember to top it off with fresh water only.
After about two to three weeks, you should see your live rock blooming with whatever hitchhiked along with it. Now is a good time to add a cleanup crew of snails, urchins and hermit crabs.
After about a month, test the water again. If ammonia and nitrites are at zero it is probably time to add a fish! (Nitrates may take longer to reach zero, but this can also be done by changing water.)
When choosing a fish for a new tank it is usually best to get a juvenile of any species as even the most docile species tend to grow more aggressive with age.
Do some research on fish compatibility, and add 1-2 fish at a time until your tank bioload is maxed out. The more fully-cured live rock you have in the tank to start, the more stable the tank will be.
There are some excellent forums on saltwater tanks out there. One of my favorites is reefs.org, but there are others. The key to success in the hobby is learning more about it, before spending any $!
Here are a few of the soft corals I keep in my tank.
The Bangaii/Kaudern's Cardinal likes to hang out near (and sometimes in!) the long-spined urchin.
Thanks for checking out my guide!