If you are self employed it is easy to forget to put your prices up. When you consider how much prices tend to increase over a set period, then it makes sense that you also should be doing the same. The average salary usually increases by about 2 -3 % a year to keep in line with inflation but as a self employed person, you need to make sure that you do this to keep your profit up as your expenses become higher.
Making clients aware of a price increase should be done well in advance. Explain to them why this is necessary, such as an increase in the price of materials so therefore you need to increase your sales rate, or even the fact that you are now having to put in more hours than previous as the jobs they require have become harder to do. This is often the case when working for a growing company.