You can support yourself. Your income needs to cover your living costs without relying on state benefits. This is checked for you and, where relevant, your family. Having proper health insurance is part of this.

Your identity and nationality are clear. The office needs to be sure who you are and where you are from.

You hold a valid passport. You normally need a valid passport or an accepted passport replacement.

There is no reason to refuse you on public security grounds. For example, serious criminal matters can stand in the way.

You entered with the correct visa. If your stay needed a visa, you should have entered on the right one and given correct information when you applied for it.

Some permits soften some of these. Certain permits, especially family and humanitarian ones, have their own rules that can reduce or waive a condition. For example, the livelihood condition is treated differently in some family cases.

Supporting yourself is taken seriously. This is the condition people most often stumble on. A shortage here usually cannot be waved through, so it is worth getting your income and insurance in order before you apply.

A sponsor can help in some cases. In certain situations a formal undertaking from someone who agrees to cover your costs (Verpflichtungserklärung) can be part of showing support.