Many people things, logo is nothing but the symbol or may be the way the name of company appears. The logo is a specific pattern to define company identity which is acceptable on any surface. In earlier days, Logo were more critical or jazzy to look different, but now days the era has changed, companies want their presentable symbol come logo to simple, to make if cost effective for future. For example if company willing to print on stationary, the more logo is difficult the more it will loose its visibility on other surface. Logo should not just appear nicely on screen, but on merchandise too.
Selection of logo color must be relevant to type of business, for example if the logo is related to Medical then the color selection would be, Light Green, Blue, Light Blue, etc. for IT, it will be Dark & light blue combination, if the brand is related to children then it would be spot colors like Red, Yellow, Orange. Most of the advertising agencies are falling such type of thumb rule.
Selection of symmetrical geometrical shapes would help the placement of logo anywhere in future, there is no rule to not use any other shapes to create logo but then you need to make sure it needs to be easy to handle and does not look like falling apart. Advertising agency needs to take care this.
Logo playing a major role on office stationary and other official communication like, on Advertising Material, Letterhead, Product, Business Card, Email Signature, Profile picture of official email, IM, systems, Invoices, etc.