Write out the entire equation, without separating the compounds into their ionic components. For example, the problem may tell you that hydrogen chloride reacts with potassium hydroxide to form water and potassium chloride. The chemical reaction that corresponds to this is HCl + KOH, giving you H2O + KCl.
Examine the solubility rules, and determine whether each of the reactants and products is soluble. The main solubility rules state that the group 1 elements form soluble compounds; the group 2 elements are not soluble when combined with fluorine; Cl-, Br- and I- are soluble except for when combined with Pb+2, Hg2+2, and Ag+; compounds with CH3COO-, ClO3-, ClO4-, and NO3- are soluble. Compounds with OH- are also insoluble. Therefore, HCl is soluble, KOH is not soluble, H2O is not soluble, and KCl is soluble.
Write the total reaction with the proper reactants and products being separated into their component ions. Since HCl is soluble, it is written in ionic form. Since the reactant KOH is a strong electrolyte, it is written in its ionic form. Since H2O is not soluble, it is not written in ionic form. Since KCl is soluble, it is written in ionic form. The overall equation is
(H+) + (Cl-) + (K+) + (OH-) gives you H2O + (K+) + (Cl-).
Cross out the ions that appear on both sides of the equations. These ions do not need to appear in the net ionic equation. For example, K+ and Cl- appear on both sides of the equation, so cross them out.
Write the final net ionic equation. Writing the equation without the crossed out ions gives you the net ionic equation. The final result of the problem is (H+) + (OH-) gives you H2O.