Ask yourself “Does my marketing material hit a home run?” What are your bragging rights?
Remember the last time you saw a Geico ad or a Telus ad -- they are very memorable aren't they? Marketing material is not just about cute geckos and colorful bugs and flowers though. They are all part of a way to communicate your brand. And it works for small businesses as well.
Take a look at your proposals, invoices and business cards -- do they have any commonality between them? Or were they designed in the heat of the moment. Just spending an afternoon aligning the look of all those 3 documents (and maybe a bit of your website) you'll do yourself a huge favor in terms of consistency.