Marine tanks take a lot longer to cycle than a freshwater one, so have patience. It can take anywhere from 2 to 6 weeks before livestock can start to be added.

Make sure you have enough live rock or media that can house the beneficial bacteria. A good amount of live rock to have is 10% of your water volume, so 20kg in 200 litres for example. This can be found at local fish stores or from private sellers. Check for pests!

Choose a suitable filtration set up for both maintenance ease and quality of filtration. Its always best to over filter than try and push everything to its limit. External filters or sumps are common in a marine set up and allow for extra water volume, also noisy skimmers and reactors can be hidden from view. You will be regularly maintaining this so its best to arrange pipework and place everything in an easy to access way so it makes it easier for you and less risky for the set up.

Several cm of coral sand or suitable substrate should be placed on the bottom of the tank. Once you have your sand/ substrate in place and your rock secure, you can fill it with salt water (1.025 is the salinity level for most marine tanks) and leave it to run with 12 hour night/ day cycles. Local fish stores may sell salt water and RO water (Reverse Osmosis) as you will not want your tap water anywhere near your marine tank. You can make your own but will need to use an RO Filter on your tap water before adding the correct marine salt to it. The RO water is also used to top up the tank so when water evaporates during the day, the salinity (salt level) doesn't increase so make sure you have enough on hand at all times. 

It's also good to use this time to check where the flow of you tank goes to see if it creates dead zones (an area where food or waste may get trapped, build up and decay). Using a wave pump will help this process a lot and is worth investing in.

You can add beneficial bacteria such as Reef Balance to speed up the nitrogen cycle but you must test your water frequently, making sure ammonia and nitrite are zero before livestock is added. Invertebrates such as hermit crabs or shrimp are great first additions before actual fish as they produce far less ammonia and your clean up crew gets established first so they can clear up after new additions. Make sure ammonia and nitrite are zero before adding new fish and corals, and check with your local store for compatibility advice.