Bridges come in all shapes and forms honestly. Some people modulate up...some people modulate down a key or a few. Some bridges stay on the same key yet slowly add harmonies to build up. It's all kind of luck in reality. You're singing/writing the song and usually stumble into the idea. If i could tell you how to exactly do it...i'd bottle it up and sell it! LOL. The only thing I can assure you is that it needs to set up either the introduction or re-introduction to the chorus therefore it gets treated like a passing chord...it's your "bridge" to what your trying to finally say and establish. Most people like to keep a bridge a easily repeatable and catchy thing that people can attach to and serves as a notice to say..."look HERE the chorus is coming!!" I will say this though..if your bridge is better than your chorus...your in real dog poop!. I've seen that countless times and the song falls flat on its face.
"you bust your ass to make all the money you can...thinking it solves shit...and then you realize..when and if you get there at all...you got more problems and you missed out on the one thing you can't buy or get back...your life! Spend time with friends and family...You can be broke in other ways too!...."