For logo design lots of people making some mistakes which are really ruined their logo making, this is why you should have to make your logo by your own style dont copy it from others but you can take concept from others. Customer choice is very important here sometimes logo makers cant understand the taste of the customer then problem is arise, so it should be fix. Compete with your competitors watch them which successful methods they are using, But dont copy from them because of it'll ruin your logo making. Colors and fonts are very important here, suppose you use lots of color and fonts in one logo then it wont looks good whatever it should be, Beside it, it will cost you up when you're going to print the logo. Make the simple logo design that people can understand easily, complexity can hamper your design.
So, these are some common mistakes which should be avoid as a logo designer.