1. Unskilled use of dodge/burn to do shading. It never looks good, it just looks as though your characters are made of shiny plastic.
2. Excessive copy/paste. Now and again it’s alright, but when your comic strip consists of the same frame copied/pasted 5 times, it gets a bit boring to look at.
3. Bad scanning. Clean up your scans people. If you’re going to use hand-drawn art, make sure it looks nice. If you’re using scanned lineart and digital colouring, for the love of god learn how to colour underneath your lines and don’t just use the fill tool. It leaves those awful white parts between the lines and colour.
4. Stick figure comics. There are notable exceptions to this one - xkcd.com being one - but for the most part it’s just lazy. xkcd gets away with it because each frame is hand-drawn, and the characters actually have body language drawn into them.
5. Gigantic images. Learn how to resize things for viewing on-screen.
6. Watermarks. Nobody wants to steal your shitty comic, get over yourself.
7. Translucent white speech bubbles. Seriously, why do I keep seeing this? Just because photoshop can make things semi-transparent doesn’t mean you should do it. It looks tacky and makes your text hard to read.
8. In-jokes. If I need to know something that happened to you and your friends the other day to get a joke, don’t put it on the internet.
9. Blatant ripoffs. How many clones of cyanide & happiness are there? Hundreds. Being inspired by something is one thing, but just copying the entire idea and art style is too much. Come up with something original.
10. Beautiful artwork and lackluster storytelling. Get a writer if you need to, but there’s nothing worse than this waste of talent. I’m a little guilty of this one too myself, which is why my comics always end mid-story.

So there you have it. Steer clear of these, and you’ll have me as a fan every time.