A lender will want to verify your income and asset documentation at the outset. Yes, your loan application will state how much money you make and how much money is in the bank but you will be asked for certain pieces of information so it's best to gather that information before you apply for a mortgage.
You'll need to provide your most recent paycheck stubs covering a 30 day period that also shows year-to-date income. That means most recent and it also means that if you get paid every other week you'll need to provide three paystubs instead of two. If during the approval process another payday has passed, keep that paycheck stub because a copy of that will need to be included in your loan file. You will also need to provide your two year most recent tax returns and W2 forms.
To document sufficient funds to close on your transaction, provide only the bank or investment statements from the accounts you'll be using in order to close on your application. This also means include all pages from your statements, even if some of those pages are blank. Finally, make sure that your application is 100% complete, with signatures where they need to be as well as places where your initial is required.
By having all your initial documentation along with your loan application, your loan will be processed much more quickly giving you plenty of time to close on your transaction.