While the variables are infinite (that's a good thing - it means that every logo can be unique) there are certain benchmarks (I hesitate to call them rules) that if you follow, will pretty well insure that you'll end up with a decent and workable logo. While whether or not a logo is 'good' remains completely subjective, following these pointers will give you a logo that's usable, practical and promising a long shelf life.
Your logo should be able to stand out as completely 'yours'. It's surprising how many times we get asked to 'copy' logos - we've even had clients request a 'version' of my brand. Not a good idea. On top of the potential legal complications nothing screams 'unprofessional' like a logo that's looks even remotely like someone else's. Do not copy. I'll say it again. Do. Not. Copy.
Every few years there's a trend, or fad, that new logos seems to embrace. A few years ago it was the 'swoosh' - made logos all hi-tech and 'internety'. Trouble is, everybody jumped on that bandwagon and the treatment rapidly became hackneyed and trite. Few years hence, and we've got lots of people stuck with out of date designs. The latest design logo trend is so-called 2.0, a technique that (like a lot of design trends) can be traced back to Apple Computers. Take your logo, add a 'gel' treatment, give it glassy reflection at the bottom and you're all set. (hey - the 3D version of our house could qualify). Web 2.0 is still going strong, but I'll go out on a limb and say it will be yesterday's news by end of summer.
3) Gimmick Free
Special FX and filters are usually applied, by inexperienced designers, to logos that are 'missing something'. Trouble is, what the logo is generally missing is any design integrity, and adding bevels, lens flares and drop shadows is the logo design version of 'putting lipstick on a pig'. While it certainly shows how cool the latest design software is, it doesn't do much for the professionalism of your mark. Such treatments are fine for glamour shots (used as display pieces on brochures and the like) but are only going to cause grief down the road, especially when it comes to application of your new logo on standard business material. Your logo should be as technically simple as possible for adaptability, which just happened to be number 4 on our list...
Over the life of your company, you'll want to plaster your logo over everything you send out. That's the point of having a logo in the first place. In order to do this, you'll need a logo that's adaptable to every occasion and while they may look 'pretty' , the design gimmicks we just talked about render your logo impractical for many of these uses. Some of these uses - checks, FAXes, embroidery, newspaper ads, invoices, letterheads, etc. Your new logo has to work on all of them. You'll also need a quality black and white version that can reproduce as a halftone grayscale, or in the cases of low-resolution BW reproduction, a linear version.
When using your logo, you'll need to be able to use it small. Real small. Postage stamp size. Classic example of this - over the years, I've designed a load of sports event posters that feature logos from dozens of event sponsors. Space only permits the logos to be featured as very small images and it's always the simpler logos that stand out when viewed from a distance. The cluttered logos aren't recognizable to any great degree and the sponsors are probably wasting their money, especially if inclusion on the poster is the only benefit of their sponsorship. When it comes to scalability, the text portion of the logo is the most important, as that's the piece you want people to remember. Scrawny, sickly text doesn't read very well at half an inch high.
6) Color is Secondary
Colors are extremely important. Using consistent corporate colors will become part of your brand - that's understood. However, when it comes to the design of your logo, color must always be secondary. A logo that requires color to 'hold' the design together is fine when reproduction is optimal - websites, 4 color process printing and what have you - but even then only if the size is appropriate as well. Logos that rely too much on color tend to blend together when used small (see above) and unless the contrast between the two colors is pronounced, will be a grey mess if used in black and white. As for low-resolution reproduction (FAXES, checks, etc) you can forget about readability completely - logos that use color as a design cornerstone usually come out as black blotches on a FAX transmission and with all their money, banks still haven't figured out how to print a decent check.
7) Appropriate Aspect Ratio & Footprint
The aspect ratio of a logo is the relationship between a logo's height and it's width. Bottom line, you don't want a logo that's too tall, or too wide. Square'ish' is always best as this allows the maximum adaptability of a logo, especially when it's being used in conjunction with other artwork. The 'footprint' of a logo refers to the amount of physical space that's required to place a logo on any page. If the footprint is 'wonky' - trailing design elements 'poke' outside the footprint - it can greatly affect the size that the design can be used at, as well as the visual impact of same.
Like most 'rules' of design, not all of these will apply in every situation, and in many cases, we'll toss them out completely. However, they should give you a road map that will help you navigate the sometimes frustrating creative process to design your new logo.