Portrait of the client should be in any case before the preparation of the advertising company. It is necessary to determine to whom and where we will show advertising.
For offline business important parameter such as the geographical location of the client. Show ads in one city, and have an office in another is not very effective ( if you do not have an exclusive offer).
For online geography also matters. You need to consider the features of language, time difference, the mentality, the financial position of a potential client.
Sex has a huge importance when making a portrait of a client.
Women buy on emotions. Give as many descriptions of the emotions they will get and they will buy fast, a lot and expensive.
Men buy if they logically understand the benefits. They also approach the process of buying from a critical point of view, thoroughly weighing the pros and cons.