Four important things to be aware of before going to a studio.
1) Copyright : You should always be in control of your content i.e your lyrics. Whatever lyrics, thoughts and ideas you have, you should write down and email it back to yourself.
2) Price arrangements: You should also have a set budget for your song. A lot of producers tend to exaggerate about certain productions and have artist pay more than expected. So think about a suitable price range and stick to it. If the studio has a set price, even better.
3) Credibility: Research the studio or the producer you will be working with. See what work they've done before, who they have worked with in the past. Listen to see if they would be a good fit for you.
4) If there should be any contracts involved. DO NOT sign without fully understanding what it is on the paper.