The only really bad habit that any of mine ended up with is scratching on wood. That one was partially my fault though because I didn't get anything acceptable for him to scratch on that he liked until recently. I had tried several things, but never sisal for some reason. I got a sisal scratching post and he started using it right away.
Here are a few things I did do that I think helped. . .
1. I harness trained all of mine from the time I got them. Now they are all easy to get into a harness, this helps when I take them to Petsmart.
2. I take them all to Petsmart (not at the same time of course). I started doing this as soon as they had their shots (and their vet is at Petsmart so they were exposed to the noise and stuff beforehand). This helped them all get comfortable with people and other pets and I only take one at a time so it gives me some special time with one of my kitties
3. I take them outside on their leashes (Mercury actually walks around the neighborhood with me). Usually I just use the long lead and let them explore and sometimes I hook them up to the front porch. . . They LOVE this, and I think that it helps them become familar with their territory. They never go outside alone, and they know that. I don't normally have a problem with any of them because they associate the harness with outside. No harness= no outside because I have never taken them out without it, even if they are in a crate, their harness is on.
I thought of a few things that I wish I had done, and will start to do now.
1. Found more cat friendly dogs. I had a few come over, but one was not very friendly and the other was rather young and too hyper. . . I did have a friend's dog living in my basement for about two months, but I didn't do much to get the cats used to him. He was in the basement most of the time because Mercury REALLY didn't like him (and the dog, who was not small, was scared of him) and because the dog had decided that no matter how much I took him outside, he had to use my house as his bathroom. Anyway, I am not sure how my cats will react to a dog now.
2. Had more people in general come over I guess? I don't know, it's the wierdest thing, none of my cats are really scared of people at Petsmart, but for some reason, Nemo and Bentley still run and hide whenever anyone comes over, unless they have known them for quite a while.