Although informal essays are generally written more for fun than because they have been given as homework, it doesn’t mean you shouldn’t select informative topics for essays. The subject matter of your essay should not only be interesting, but also important, significant not only for you, but for the ones who are going to read it as well.
Informal essay writing, as it is understood from the name, mostly deals with relaxed and witty exchange of opinions; the norms are less important than in other kinds of writing, because the very idea is based on their absence. It means that it is exactly the kind of writing in which you are allowed to express maximum level of personalization. Study the examples of informal essay on the Net and you will see the point.
It is rather useless to try and enumerate some set of rules on informal essay writing, because the only rule one can think about is to write without following any particular rules. However, it doesn’t mean that you should take pains to sound more informal than you normally are. The informality isn’t imposed on you; it simply means that there are fewer restrictions than there are usually. Avoid slang – it usually makes you sound not informal, but simply sloppy.
And, of course, try to find and use informative topics for essays, for the idea behind informal writing is not the importance of informal communication, but an opportunity for you to express your opinion without restrictions of formal style, tight regulations and so on. Try to speak about the theme that is important for you in a way you speak about it with your friends who are also interested in it – it may be a good indication at what kind of writing you should try to achieve.