Many variations possible for this, depends the type you like and if you want just a few larger ones or a lot of smaller fish.
If you are wanting to put a mix of tetras that would be fine, you would want to keep to a mix of the smaller tetras for that size tank like the Ember Tetra, Neon, Cardnial, Glolite and flame tetras.
You could also add in a couple of Kuhli loaches and corydoras to help keep the base clean or some Red and yellow cherry shrimp.
The amount of fish will depend on what type you choose.
Many variations possible for this, depends the type you like and if you want just a few larger ones or a lot of smaller fish.
If you are wanting to put a mix of tetras that would be fine, you would want to keep to a mix of the smaller tetras for that size tank like the Ember Tetra, Neon, Cardnial, Glolite and flame tetras.
You could also add in a couple of Kuhli loaches and corydoras to help keep the base clean or some Red and yellow cherry shrimp.
The amount of fish will depend on what type you choose.