1. Do be fully honest with your loan officer about your situation, because if it's not what you say it is, underwriting will find out, and it's much better for your loan to fall part during initial discussions with the loan officer than to fall apart after you've spend money on an appraisal, home inspection, earnest money, etc.
2. Do review the good faith estimate, application, as well as all disclosures, first on your own and start writing down questions, and then secondly with your loan officer so you fully understand the information you are signing as well as can get all of your questions answered.
3. Do read the final documents before you sign them, not after, as the documents are legally binding and there isn't always a "cooling off" period.
4. Do continue to use your credit as usual
5. Do continue to work at least the same amount of hours
6. Do call your loan officer with any questions, their primary goal is to make sure your loan goes smoothly even if it means giving you news you may not want to hear. Better to know early on if something is going to be a problem rather than waiting until the last second.
7. Do end all disputes on your credit report prior to the credit check
1. Do not obtain any new credit or close any existing credit after your credit report has been checked and before you close on the loan
2. Do not deposit any funds into your account which are not normal payroll deposits until you first discuss with your loan officer
3. Do not miss any payments
4. Do not change your employer or employment status during the mortgage transaction
5. Do not let your savings/checking/assets-that-are-being-used-to-qualify balances decrease without first discussing with your loan officer; this would include spending money on moving costs/new furniture/turning on utilities at your new home, amongst other items.
6. Do not pay off collections/charge-offs (especially ones over 2 years old) during or shortly before the mortgage process without discussing with your loan officer first, as it can update the date of last activity and bring down the scores quite a bit. If they need to be paid, it's recommended you DO pay them off through the closing/escrow on the mortgage transaction.
7. Do not submit an offer on a home without first discussing with your loan officer what you intend to offer - items such as repair credits, personal items being sold with a home, and closing dates all can impact the mortgage.
8. Do NOT go on vacation or plan any vacation whatsoever during the entire transaction.