This article was posted on the Smashing Magazine website and it is very useful. When you're starting out you tend to break one of these rules. I've broken number 5, which was designing for yourself and not the client. You always have to stick to the brief and not sidetrack. Even if you've been designing for years, it's always good to refresh yourself or maybe you can comment on how you disagree or would like to add a suggestion. Either way it's an interesting article.
Mistake #5 from the website:
"5. Designing For Yourself Rather Than The Client
Never impose your own personality onto a client’s work.
You can often spot this logo design sin a mile away; the cause is usually a designer’s enormous ego. If you have found a cool new font that you can’t wait to use in a design, well… don’t. Ask yourself if that font is truly appropriate for the business you’re designing for? For example, a great modern typographic font that you just love is not likely suited to a serious business such as a lawyer’s office.
Some designers also make the mistake of including a “trademark” in their work. While you should be proud of your work, imposing your personality onto a logo is wrong. Stay focused on the client’s requirements by sticking to the brief."
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