The important documents required are identification, employment details, bank account details, debt information, a proof of financial assets and also proof of other income sources if any. (syndicatemortgages.com)
So rather than purely depending on book sales for income, it opens a lot of other income streams for you. (amyharrop.com)
First, see if you can increase the amount withheld from your pay from other income sources. (thebalancesmb.com)