1. Fight for what you believe
Bill Watterson wrote and drew Calvin and Hobbes for ten years, and in that time he went through some almighty battles. The distribution studio that effectively owned the rights to his characters wanted to make a cartoon, and to sell related merchandise, but Bill didn't want an actor putting a voice to something people could imagine. He didn't want toys and gifts to weaken the world of the strip.
Bill fought a long and difficult battle, the studio contract was so one sided they could have fired him and hired writers to continue the strip. Eventually though, he won the battle.
Too often we let great ideas go because of one piece of rejection or criticism. If you believe in something then fight for it. A great example of this is on Andrew H's blog here.
2. If the system is wrong, change it
Calvin and Hobbes was a playful and creative strip, but it was heavily restricted by the norms of cartoon publishing at the time. The Sunday strips had to be made of blocks in set places, losing the first two boxes to a throwaway gag.
Bill fought for a change (which in some cases meant the strip lost space in publications) which allowed the strip to be one whole piece, providing a huge increase in creative scope. It allowed such wonderful strips as this one:
In marketing we are always talking about things that need improving, so let's improve them.
3. Know when to stop
For most successful comics, ten years is quite a short production time. However it does stop the decaying quality that comes with trying to stay original for many decades (Simpsons, Garfield, etc). By stopping before the ideas ran out Bill Watterson preserved Calvin and Hobbes as a strip that never lost it's edge or sparkle. The reverence it is held in by many has proved Bill right, even if it was sad to see them go.
Too many campaigns carry on past their use by date, we should be as observant about quality as any other creative medium. Don't carry on just because we can, but also don't stop while something is still yet to peak.
4. Treat people with intelligence
Many cartoons treat people as if they are stupid. They highlight every joke and make out that the readers have no intelligence and cannot work things out for themselves.
The worst offender for this is the awful Mandy in the Daily Mirror. Which (until recently at least) used to mark every key word that you were supposed to laugh at in bold and italics.
Calvin and Hobbes never shied away from deeper topics, and beneath the humour was one of the most intelligent and meaningful commentaries on the human existence there has ever been.
In marketing, too often we forget that people are human. They have brains, they don't need to be spoonfed everything, they should not be treated as 'consumers'.
5. What you don't say can be as important as what you do
Sometimes not saying something can be far far more powerful than saying it. Take being stylish, as soon as you say 'We make stylish...' you make it seem less so. Know what to say, and what not to say.
Calvin and Hobbes never answers the questions of its reality. Hobbes is both real and unreal, you are left to decide for yourself the full story.
Likewise you never know the names of his parents, they are just 'mom and dad', which makes them so much more identifiable as characters.
6. Quality lasts
The legacy of Calvin and Hobbes is huge. For many (including me) it becomes a treasured part of life that weaves itself around you. Almost everything I ever do has a reference point in the strips, it asks questions and makes observations that still speak wisely about the world almost 18 years after it finished.
If you make something you can be proud of, the results and legacy will always be better than if you let yourself move downwards.
These two strips are two of many that are completely relevant for those of us in marketing: