It is regular knowledge that you shouldn't bring any fish first to your home until you finish securing your freshwater aquarium tank first, and the other things needed before you can actually bring these fish into your home.
Check the tank for leaks Testing your tank for leaks is very easy, you just have to fill it with water and see if the water in the tank leaks in any way.
If there is none, good, but have your silicone-based sealant ready just in case there would be leaks.
It is important to test it again in case you found a leak, in order to check if your sealant has sealed the leak properly.
Decorate your aquarium You can now proceed to decorate your tank.
There is actually no restriction for this.
Just be sure that the decoration's composition would not make drastic changes in the water chemistry.
As for the substrate, choose one that can regulate the water pH level of the water effectively.
Rinse all decorations first with warm tap water before finally putting them into place.
Prepare all necessary equipments Make sure that each component is nicely placed and works properly.
Make sure that there aren't any broken parts that might disrupt the equipment from working properly.
All electrical cords should be properly grounded, and should be fairly safe from anything that might cause them to get wet.
It is recommended that you apply water conditioners at this point, to de-chlorinate the water for the early development of the much needed bacteria for biological filtration of your filters.
After setting all of the necessary equipments, try to turn them all on, as if there are already fish in the tank, and check for vital errors and fix them if necessary.
Finally, cycle the entire tank By letting the aquarium have the much needed beneficial bacteria.
This process, known as cycling, can be done by fixing the water chemistry needed for the fishes to survive, and this, in turn, can be done by taking a gradual number of steps over time.
Turn all lights off in the surrounding area of the fish tank, and then add a few drops of pure ammonia in the water.
Check if the water has about 5ppm after 30 minutes of exposure.
After one week, check the water chemistry again; if the nitrites have already started to rise, and if the ammonia levels are lower than the nitrite levels, then add more drops of ammonia.
Wait again for a few weeks, and you will see the nitrate levels start growing.
At this point, the tank is now ready to grow the beneficial bacteria.
Change at least 25% of the water in the tank, to make up for the evaporating amount of water and for the loss of chemical substances.
Again, wait for a few weeks until a white cloud appears on the water, and wait for it to disappear.
Your tank has now finished the whole process of cycling, and your freshwater aquarium setup is now complete.
This can take very long if done from scratch, but you can always call your local hobby store, which can provide you with a tank already thriving with beneficial bacteria.
This will certainly speed things up.