What tips do you have to prepare for an oral exam?

It slightly depends on the exam board, but if you're able to prepare your answers in advice make sure you know your responses inside out! An oral exam can be a stressful environment so the more familiar you are with your answers the less likely you are to have a memory slip. The easiest way to memorise it is to make sure you allow plenty of time so you can learn it in little chunks and build it up over time. I would also advise that you try not to be too ambitious with how long your responses are - you don't want to feel pressure to speak at a ridiculous speed just to get it all in! It's better to include a bit less information but speak in a more understandable way. You also need to make sure you understand what you're saying - it is a lot easier to memorise a text if you know what it is that you're wanting to say (also you will be unable to deliver the response in a convincing way with appropriate use of intonation if you are just parroting a text that you have learnt without understanding a word of it.).
To help with pronunciation I would encourage you to listen to French podcasts (e.g Grand Reportage), watch French youtubers (e.g Cyprien) or French movies and series (e.g Dix pour cent) on Netflix!