Don't ask outdated and ineffective questions, particularly brain teasers. That doens't test if someone will perform on the job, only that they know brainteasers and/or they had time to prepare specifically for that type of interview.\
Not everyone does their best work in fast-paced high-pressure situations. aka whiteboard programming is not for everyone. They like to chew on questions and go through different processes to get there.
The best way to see how someone works is to... work with them.
Share questions in advance.
Use a real problem.
Give access to data.
Make it interactive.
Follow a single scenario?
Hold feedback until the end. Don't let one person's review anchor everyone else's before they can make their own objective judgement.
Give feedback on the process, too. Collect it at the end of each interview loop, what worked or didn't work in the process.