A good application letter follows a formula. It must always contain the following information: the sender, addressee, place and date, salutation, reason, motivation, suitability, conclusion with signature, and your CV. Phrase your motivation and suitability in a positive way.

typed or handwritten? 

An application letter should stand out for the right reasons. It has to invite someone to read it. A handwritten letter isn`t always easy to read and it is not very contemporary. That is why you`re better off typing your cover letter and CV. 

avoiding mistakes 

Many people stop reading a letter as soon as they run into a mistake. So check your letter carefully for errors in language, spelling and typing. While a word processor`s spell-checker will catch most mistakes, it is never foolproof. If possible, have someone else read through your letter. Using a fresh pair of eyes is often worth the effort. 

who should I send it to? 

Usually a job advertisement will state who the letter should be sent to. If it does not, or if you are writing an open application, then check with the company first. That shows that you have made the effort and stops your letter from going to the wrong person, which may lead to it getting lost, or even being thrown away. Do not forget to ask for the person`s initials, as well as the correct spelling and their job title.