The writer's mission in writing the informal essay is to portray something -- an event, an idea, a problem, a situation, a decision, or a memory. The writing should be pursued in a relaxed and casual manner. It should carry a carefree and conversational tone. But it must also maintain a solid foundational structure. Writing informally is far from academically ordered, but it is in no way permissive of sloppy design.
Preserving a strong sense of personality is key in composing the informal essay. It can be funny, but it doesn't have to be. It could, instead, be entirely somber. In essence, the informal essay is a story, and as such the creator or author is allowed to adorn the essay with all sorts of notions, be they true or wholly nonsensical. Even time and space can be fictional. A story does not require honesty by any means, but it must be entertaining. Writing creatively, with personality, supports that intention.
There are specified manners in writing, as there are in speaking, which signify a formal or informal atmosphere. Colloquialisms are widely used and completely acceptable in informal methods of writing. The use of contractions in casual composition are tolerated as well, but should never be found in a formal assignment. Clichés are also welcome, as is the use of an imperative and/or active voice. Formal text, however, requires a passive voice as opposed to an active one, and an imperative voice is never permitted. When writing informally, it's also perfectly satisfactory to write in the first, second, or third person. But for a formal structure, use of only the third person is permitted.
An informal essay is distinguishable not only by its subject matter, but even more so by its tone, which is always unassuming and casual. More often the formal essay is aimed at educating its reader on a specified topic or it might even be attempting to provoke a desired opinion. And while the informal essay could also encompass these aspects, it would only do so without regard to the outcome, either way. This unimposing manner of writing creates a more intimate relationship between the writer and the reader. There's a sense of familiarity that inspires the reader to further immerse himself into the story or essay.