Welcome to the salty side! Hopefully before you have made any purchases, you have already read and have a decent understanding of the hobby. Below are some steps that aim to provide enough knowledge to get you started. This is not the END ALL BE ALL. There are so many ways to enjoy the hobby and this is my personal way of getting started.
NOTE: The phrase "knowledge is power" is probably the most relevant saying when referring to this hobby.
Step 1.) If there was one thing I wish I would have done when I started this hobby, it would have been to pick up a well reviewed book about marine life keeping. "The Conscientious Marine Aquarist" by Robert Flenner would have helped tremendously! One needs to have a pretty good grasp of the nitrogen cycle in an aquarium before getting started.
Step 2.) Understand the basic parameters that need to be monitored to keep a saltwater FOWLR (fish only with live rock) tank first as you wont be putting coral in it for at least a few weeks. If you are planning on putting corals in the tank you should monitor with the ideal level in parenthesis:Temperature 77-82f,(78f) PH: 7.8-8.2,(8.1) dkh:8-11 (10) Salinity: 1.024-1.026(pick one and keep it stable), Calcium 400-450(420), Magnesium 1250-1400. Ammonia 0, Nitrite 0, nitrate 0-30 (depending on what corals) and phosphate 0-.1
Step 3.) Buy some stuff! Now you are ready to purchase some items! I would purchase test kits for ph,dkh,ammonia,nitrite,and nitrate and a refractometer for salinity. I would buy your tank, if you are purchasing one over 30g i would recommend getting a sump with a protein skimmer instead of other choices of filtration.Your choice of rock (i always use reef saver rock from brs as it has no pests). There is always the option of live rock, but there are pros and cons associated with each choice of rock. In my opinion, the most cost effective is cured dry rock. The best option if you can afford it, is dry rock that has been made live in its own system, as this will assure there are no pests. Circulation pumps, look at the gph rating associated with each pump. the aim is to have at bare minnimum, a 10x tank turnover ratio. What this means is that you pumps will push ten times the water volume of your system. For example, if you are getting a 50g tank, you want a bare minimum goal of 500gph split between two pumps (2, 250gph pumps). i always recommend being in the 20x turnover ratio to start out. If you have a sump, your pump should also be 10x the turnover through the return, giving you 20x turnover total.Sand- i like to use dry aragonite sand but there are other options that work as well. Salt- get a reef grade salt mix such as Reef crystals, red sea coral pro, kent marine reef salt, live aquaria reef salt, and there are multiple others that work well. Finally! I would recommend getting an RODI unit. You can always buy RODI water from your local fish store or premixed saltwater. Making your own will save a lot of money in the long run, trust me. There are some budget options available such as the RO buddy as well. My personal preference is the BRS 5 stage. A Source of Ammonia- to get the nitrogen cycle going you will need a source of ammonia. I would recommend doctor Tim's ammonia. It has directions for you to follow. So, to start out, a tank,sump,skimmer,rock, salt,sand,rodi unit,a source of ammonia and circulation pumps are all you need!
Step 4.) Add sand, rock, saltwater, and circulation pumps and if you have a sump, you will need to plumb it to the tank (there are so many good threads on drilling and plumbing a tank that i won't get into). To begin the nitrogen cycle, you don't need lights. After you have your system running and the clouds from the sand disappear, it is time to add ammonia! You can use a bunch of fish food however, DR.Tim's ammonia is a method that has so many success stories.
Step 5.) If you are not using Dr. Tim's, add the fish food or source of ammonia. Wait 24 hours and measure your ammonia and nitrite. When i started out, i measured ammonia and nitrite once a day, every other day for 2 weeks while feeding the empty tank on the days i dont measure (a small pinch will suffice). After two weeks you may or may not see that you have some nitrites, its time to start measuring ammonia and nitrate if you have a measurable level of nitrite . Once you notice you have some nitrates, you are close to being able to add a fish! Your cycle is complete once you can feed the tank, and within 24 hours you will see 0 ammonia and a small increase in nitrate!
Step 6.) Pick out a light fixture that goes with your goals! if you want higher light demanding corals, you'll need a pretty strong light. My recommendation, get the best lighting you can afford that has a dim feature. This will allow you to get higher light demanding corals later on. It does not make a whole lot of sense to buy a crappy light, then sell it for half of what you bought it for and then buy a nicer light that you should have just started out with.
Step 7.) Go get you some fish! Visit the local fish store, browse the web, or ask people for recommendations on fish. DO NOT impulse buy fish! I would recommend going to the fish store and write down names of the fish you like. Then, go home and research everything you can about that fish. Go and choose 1 fish at first.
Step 8.) Monitor you ammonia, nitrite, and nitrates for 2-3 weeks after your first fish addition. If you have 0 ammonia and 0 nitrites and an acceptable level of nitrates you can go pick one or 2 more depending on the size of your tank and the fish that was bough previously.
step 9.) My personal preference is to stock to your liking/ what the tank can reasonably handle before getting coral. The main reason i do this is it allows me to know what my parameters are before i add coral. If you add coral in the mix of getting fish, it becomes a balance game to keep the corals healthy while keeping ammonia and nitrite down after new additions.
Step 10.) Go pick out some easy to care for corals!
There you go! you've started your first reef tank! Always remember to research what you are wanting to buy before you buy it! After you start to add SPS corals, you will need to monitor calcium,magnesium, and alk much more frequently. I hope this helps!