You're mixing sulfuric acid, #H_2SO_4#, which is a strong acid, and sodium hydroxide, #NaOH#, which is a strong base.
This implies that the two compounds will be completely dissociated in aqueous solution. In the case of sulfuric acid, you have
#H_2SO_(4(aq)) -> 2H_((aq))^(+) + SO_(4(aq))^(2-)#
One mole of of sulfuric acid will produce 2 moles of #H^(+)# and 1 mole of #SO_4^(2-)#.
In the case of sodium hydroxide, you have
#NaOH_((aq)) -> Na_((aq))^(+) + OH_((aq))^(-)#
This time, one mole of sodium hydroxide will produce 1 mole of #Na^(+)# and 1 mole of #OH^(-)# in aqueous solution.
Sodium sulfate, #Na_2SO_4#, is soluble in aqueous solution, which implies that it too will exist as ions.
#Na_2SO_(4(aq)) -> 2Na_((aq))^(+) + SO_(4(aq))^(2-)#
Your balanced chemical equation for this neutralization reaction looks like this
#H_2SO_(4(aq)) + color(red)(2)NaOH_((aq)) -> Na_2SO_(4(aq)) + 2H_2O_((l))#
The complete ionic equation will be
#2H_((aq))^(+) + SO_(4(aq))^(2-) + color(red)(2)Na_((aq))^(+) + color(red)(2)OH_((aq))^(-) -> 2Na_((aq))^(+) + SO_(4(aq))^(2-) + 2H_2O_((l))#
To get the net ionic equation, eliminate the spectator ions, i.e. the ions that are on both sides of the equation. This will get you
#2H_((aq))^(+) + cancel(SO_(4(aq))^(2-)) + cancel(color(red)(2)Na_((aq))^(+)) + color(red)(2)OH_((aq))^(-) -> cancel(2Na_((aq))^(+)) + cancel(SO_(4(aq))^(2-)) + 2H_2O_((l))#
#2H_((aq))^(+) + 2OH_((aq))^(-) -> 2H_2O_((l))#
You can simplify this by 2 to get
#H_((aq))^(+) + OH_((aq))^(-) -> H_2O_((l))#