Start by outlining the achievements you have made so far and the value you add to the business. Your employer will be more open to considering an increase in salary if they can clearly see the value you bring to the table. Find out what the comparative salaries are in other similar business within your industry. Link the increase in salary to the value added to the business. If it is not possible for the company to oblige you, ask if their position can be revisited in 6 months.