There are some basic problems when people build characters. Let's see if we can handle those, eh?
Mary Sue/Gary Stu's: Some characters have too much power on one hand, and enough psychological issues to pay off a therapist's student loans. Girls' comics are filled with these characters, because not only is empowerment considered a great thing (thus the sheer number of abilities), but so is sensitivity and admitting your problems (thus the sheer number of personality problems). Another way to look at it is that they are given so much, and so must have a number of things to make up for it. There was a reason that I suggested no more than four good things and no more than two bad things; it's a simple way to balance out your characters. You should always strive for balanced characters, and should avoid characters that have too much going for them in either side of the balance sheet.
Caricatures: At the other end of the spectrum are the shallow characters, those that are more caricatures than characters. The problem is that these characters aren't intended to be serious characters, and so the writer doesn't treat them seriously. It needs to be remembered that all characters need to taken seriously, no matter how silly they are; in fact, silly characters need to be taken seriously if they are to be jokes. Think about: If you are making fun of something, you need to fully explore it, and can you fully explore something if you don't fully allow for it? Thus, you need to make sure that all of your characters are fully developed, and that characters that are caricatures show themselves to be fulyl developed in order to make your running gag go to the next level.
Disrespected Characters: Some people just shouldn't write certain types of characters. This is usually most obvious when it comes to military or religious types, or even authority figures in general, but it can apply to any type of character. The obvious example here is the character who is treated as a caricature; the FBI agent that is far too official, harasses the main character while spouting arcane laws or interpreting laws in order to nail the main characters, and is basically not someone who you want to invite to Christmas dinner. More than any other character, this kind has the most possibility of taking your readers out of the book, and possibly ruining any scene that he is in. The only real advice I can give you here is that you need to be aware of those types of characters that you don't have any respect for, and try to avoid writing those kind of characters. If you do need to write those characters, then you need to make an effort to not treat the character respectfully.
Mandatory Characters: Every genre seems to have those characters that are mandatory, and that everyone seems to make sure that they are in stories of that genres, such as the barbarian in fantasy stories or the cool alien in science fiction. The obvious solution is to don't worry about omitting the character type, and be happy about it. However, if you're using the character as part of a running gag, then see the notes regarding caricatures above.
Love Interests, Sidekicks, and Villains: Always make sure that these characters are well-developed. One of the problems is that these characters are part of the story, but combine elements of various character types as mentioned above; sidekicks may be treated as puppies, love interests may simply be elevated trollops, and villains limited to the Snidely Whiplash version. Respect these characters, as they are the most important ones to your story, and the ones that pop up the most.
Remember this advice, and your characters will love you for it!