Depending on an employer’s application process, you may still be able or even required to fill out a form by hand. If this is the case, write as neatly as you can in black ink and use block capital letters if the form asks you to.
It’s always worth checking if there is an online version of the form you can fill out instead though – making your application on-screen means correcting mistakes, spell-checking and messy handwriting are three fewer things to worry about.
Whether you’re typing or writing, never write your answers straight on to the form. Draft a version of all your responses separately, work on it again and again until it’s the best it can possibly be – and get someone else to check it for both mistakes and a general second opinion – and only then commit it to the form.