My main advice is to listen to your gut instinct. Things that mildly annoy or worry you in the interview will probably come to dominate your working relationship with them. Don't assume you can fix someone's flaws after they join. Get other people to give their gut instinct too, and everyone has a veto. When a new hire doesn't work out, it's extremely expensive and stressful for you, the person themselves, and the whole team to manage the situation, so it's better not to hire in the first place.
This means you'll need to be patient. On average, I've needed to interview 30 people to make 1 strong hire. A few extra months looking for the right person will deliver far more long-run productivity. However, treat every candidate with dignity - get back to them promptly with helpful feedback.
The best hires I've made have come through personal connections, and niche job boards. Most recruitment consultants are working merely for short-term commission, and don't care about your or the candidate's long term interests.