Use sand with an average grain size of 0.125mm, but with mixed grains.
The sand bed will be the initial biological filter for the tank and will reduce ammonia levels at later stages of the process so that added organisms have a better chance of survival.
While not necessary initially, running the return and in tank circulation will ensure the water is well oxygenated which will help to establish the necessary populations of nitrifying bacteria. Similarly, providing normal reef temperatures and specific gravity will mean less change later which can effect any organisms in the tank.
If you wish, monitor the water for ammonia and nitrite. When the nitrite has been at zero for at least a week, move to the next step. Using this method you may not register any ammonia or nitrite. If you don't, that's fine, just wait around 3 weeks after starting before moving to the next step.
The food is added to provide ammonia to start the populations of bacteria that oxidise ammonia to nitrite. The nitrite will provide for bacteria that oxidise nitrite to nitrate. Adding small amounts of food results in relatively less ammonia than adding something like a whole prawn or shrimp. As high levels of ammonia can inhibit the bacteria that oxidise nitrite, spiking ammonia can extend the period over with the necessary populations of bacteria are established. Additionally, the populations required to nitrify the remains of a prawn or shrimp may be more than is required and the populations may take longer to stabilise.
If you live in a warm temperate to tropical area you can collect your own live sand for seeding the tank. You don't need a lot of sand, but collect it from as many places as possible and also get some from other people's tanks. What you want is a diversity of organisms.
This will provide food for the sand bed organisms allowing them to reproduce and populate the sand bed. I feel it is important to have the sand bed populated with sand bed organisms rather than ones from the live rock.
During this period you can enjoy watching all the new organisms appearing in the sand bed.
Burrows made by polychaetes in a new sand bed that has just been seeded with live sand
It is good to start with a small amount of live rock first in case there is any die off of organisms on the rock. The added rock will provide more surface area for filtration bacteria and so help when more live rock is added later.
As with the first batch of live rock, adding a relatively small amount will maximise survival of organisms on and in the live rock.
It is best to have the herbivores in the tank before you start having problems with algae.
You may not have detectable ammonia or nitrate during the much of the process because biological filtration was established early on. However, it is still best to wait at least a week after completing this step to ensure some stability in the biological filtration capacity of the tank. Note that while nitrite is not very toxic in seawater, presence suggests instability of the biological filtration.