You could do it yourself but this is not advisable. You should consult a patent attorney with who has technical knowledge and qualifications in the area of the invention. Although you will most likely have all of the technical knowledge needed to describe the invention, there are particular skills in how the specification that needs to be filed is constructed that the patent attorney will be able to help with. In particular, the claims section of the specification describes the scope of the monopoly that you will have for your invention if the patent is registered and language used in describing the claims and they way they are constructed requires skill from the patent attorney. Most patent attorney firm websites will show the technical areas in which individual attorneys operate and many firms will give you a brief initial consultation without charging so that you can explain what you want to do.