i would suggest you tell us the tank and how long you plan on using the tank.
Also, when putting the water in could you give us the perimeters. I.E Ph, Ammonia/Nitrite(if any within the tank itself) Gh/Kh. As well as are you going for freshwater or Saltwater fish. as this site is good for both Saltwater and freshwater fish.
Also check out the cycling a tank area so you can get an idea on what you may need to do..
Im not an expert but i would say wait abit before putting to many fish into the tank to avoid ammonia/nitirite poisoning(i had this happen to me without getting my tank completely cycled)