A basic rental application form has to do one job: collect enough to apply your written criteria to every applicant in the same way. Everything beyond that is data you are holding for people who will mostly not become your tenants. This page is the minimum that still supports a decision, for a landlord who wants a form that gets finished.
The minimum set
Name and contact. Where they live now, since when, and who their landlord is. What they do and what they earn, as stated. Who else would live there, and pets. When they want to move in. And their consent to your contacting the referees. Under any ordinary criteria, that supports a decision you can write down and defend.
Why shorter produces better decisions
A short form is completed by everyone, which means you are comparing like with like. A long form is completed fully by the most diligent applicants and partially by the rest, so the comparison is contaminated by how much time each person had. That is not a criterion you chose and it correlates with things you must not select on.
Ask for the rest at offer
Identity documents, bank details, employer confirmation on letterhead, a guarantor's details. All of these are reasonable for the person you are about to house and unreasonable to hold for the six you are not. Splitting the process into application and offer reduces both the data you hold and the friction that loses you good applicants at the first step.
Keep the form and the criteria together
The form collects; the criteria decide. Keeping them in one place means that when you revise one you look at the other, and it makes the annual question easy: is every field on this form used by a criterion, and does every criterion have a field. Fields with no criterion are collection for its own sake, and criteria with no field are judgements you cannot evidence.
Questions people ask about basic rental application form
Is a one-page application enough?
For most residential lettings, yes. If your criteria need more, the criteria are the thing to look at first.
Should I ask for a guarantor at application?
Ask whether one would be available. Collect the guarantor's own details at offer, because a guarantor who never becomes one has had their data collected for nothing.
What about applicants without a prior landlord?
Decide in advance what you accept instead and apply it to everyone. First-time renters are a category, not an exception to be handled case by case.