Listen to everyone. Ideas come from everywhere.
What a smart cookie! I try to do this every day. From truly listening to the simple pleasantries with the grocery store cashier to the children in my life. Soaking in what others say around you has a way of triggering ideas in this good ole brain of mine.
From better ways to communicate with past clients, to new things I'd like to be when I grow up and even hobbies I'd like to entertain once I retire.
Listen to everyone. Start an idea book. Just write them down. You can go back to them later and decide if they're good or not. I keep a list of things to do, things to make and people to connect with. Most of these ideas and lists were sparked from a conversation I had with someone or heard others talk about. IE: heard while eavesdropping. Hey, the cookie says listen to everyone...
Once you stop listening, people will stop giving you ideas.