The number one thing I try to avoid being is dismissive.
First, I think dismissing ideas is the most unproductive thing to do. Nothing good can come from a lengthy personal rant about how this idea, this person or this project is doomed to fail. It always says more about you, your personality, your insecurities than about what or who you're dismissing.
Second, I firmly believe the greatest ideas look stupid at first. I'm still young but I've already seen so many cycles. It goes like this. There's a new technology/trend/idea, people laugh about it, the thing gets better, people adopt it, people forget about it, people laugh at other people who don't joint them. Here's a quote from Benedict Evans I like:
Around me, it happens on a regular basis for two things: technology and projects.
1) The new things in technology often look like gadgets, toys or simply stupid features. Or worst, useless stuff for kids who have nothing to do! One of the best examples of that is Instagram. The photo-sharing app launches. It's a toy. It's an iPhone app to help you filter photos. It's for a helpless teenager who has nothing else to do than sharing what she had for breakfast that day. Fast-forward a few years, and the app is used by the teenager's grandmother to help her plan a trip to the Maldives. By using the geolocation feature and browsing through the Tourism board hashtag, she finds the most recent pictures of the resorts she wanted to stay in. She clicks on the resort's profile, find their website and even manages to find a coupon code for a direct booking in a 3-weeks old post. From a stupid photo app to a travel agent.
2) The new projects your friends tell you about always look like a bad use of their time or a hobby at best. It goes like this. Three friends start a surfing blog and spend 10h/week on it. You take a beer with another friend and spend 3h laughing about how it is a waste of time and how you'd never invest so much time doing that because a surfing blog is not a business! Your friends keep on doing it. They learn a bunch of different things while doing it: video editing, photo editing, a bit of design and web development, writing, running targeted advertising campaigns on social media, running affiliate programs, selling online (they just turned the blog into a shop!), etc. And while you invest 3h/week laughing at them, they invest 10h/week getting better at it. The blog never turns a profit. In fact, it's a money hole. But the three friends get together to open a surfing camp in Costa Rica after being approached for their marketing skills by an investor and surf aficionado. They connected the dots. I wrote about starting as a beginner and closing the gap between your vision and your skills. I think it is an essential thought to keep in mind when starting new projects.
Anyways, I try (and will try more) to avoid being dismissive of new technologies, projects, ideas, etc. I try to be optimistic. I think it's the best way to create a virtuous circle of new ideas around you. And if you depend on ideas in your work, try to being less dismissive, it simply works.