OK, I have pontificated on previous occasions about how to deliver a good sample lesson when attending an interview. But you can spare yourself the ordeal of that sample lesson by failing to get invited for an interview.
Firstly, remember it doesn't really matter if you don't fill in the application form. We understand how busy you are: just send us a printout of your 10 page CV (listing every INSET you have ever attended) and we will cross reference it ourselves. It's not like we're busy.
Spelling, grammar and capitalisation errors are great. They show how happy-go-lucky you are and what a casual, easy-going approach you take to the written word and the process of checking over your work. They are really good indicators of how you will approach marking, planning and writing resources!
Illegibility and poor handwriting don't matter. Crossings out are not a problem. This is the era of the computer; you don't need to be able to write clearly to be a teacher.
If you are applying for an IT job (or if you mention your effective use of IT anywhere on your application) it's rather witty to back up your claims of being a well skilled in word-processing with an absolutely hopeless desk-top publishing job. Random font changes, embarrassing spell-checking errors, inconsistent indentation, inappropriate fonts... I know you're just showing me how aware you are of the commonest flaws in our students' work. And we love MS Word CV templates. They're so....unique.
Seriously, folks, it's not rocket science. If you can't be bothered to take care over an application form which I am duty bound to read from beginning to end, do you really think we will trust you with a teaching post? With, you know, real kids writing real essays and all that?