Good logo design uses colour to enhance the design and to make it memorable. Logo designers need to design in black and white as well as colour. You need to think about what happens when the colour is removed. Does the logo still work in black and white? You have to consider tones as well as colours in a design and you may need to change the contrast relationship between different elements in your design so that they still work in monotones.
A logo should be clean and modern.
The Golden (Font) Rule
A golden rule in logo design is to not use more than two fonts, but obviously there are always going to be exceptions to any rule. But in principle, it is a good idea to try and use just one or two fonts, if you want your logo design to be clear, uncluttered and modern.
Also make sure it will work on a dark background. Your client may be content with their logo design on a white background, but be aware that they may come back and require their logo to work against a dark background. Sorting that out in advance can stop a lot of hassle down the track. It is good to consider a monochrome logo at this stage too.
It’s the little things in the long run that make a logo successful.
Good luck with your next design!