What are the pitfalls?
Not having the correct documentation available
Every lender has their own criteria to determine what paper you will need to evidence for your income including how old the document can be and how many years history you need to provide. If you do not know this upfront you may find your application comes to a halt whilst you prepare the relevant information.
Knowing what income to provide
The actual figure a lender uses can vary. For example a limited company shareholder could use their salary and dividend payments with one lender, whereas another lender may be willing to use their salary and a % of the company net profit. These figures could be drastically different and can have a serious effect on the amount you can borrow.
You may have recently changed from being employed to self employed, or you may have changed the structure of your self-employment, such as from sole trader to a limited company. Whilst this may be acceptable to some lenders, this will limit your options and not knowing if your employment history is going to be acceptable to a lender before an application may cause an application to be declined.