Give yourself enough time to study for the OAT! 2 to 3 months at least. Do as many practice problems as you can because that is what makes your life easier when you're taking the real OAT. Set up a schedule for yourself for the months you're studying and really stick to it! Lastly, have a cut off time each day for when you want to stop studying, do not stay up late and sacrifice sleep because it will not help you. Do what you can during the time you have given yourself and relax outside of it.
For interviews just be honest and passionate about your answers. Don't try to practice too hard over what to say because the people interviewing you can see when what you're saying is scripted. Practice 1 to 3 days prior and just relax. Schools just want to get to know you a little bit more thats all.