Have you prepped some answers to standard questions such as "Why do you want to work here, what can you offer the firm, talk us through ax time you handled a project successfully (or similar).
Have a couple of useful questions eg about career progression or staffing structure, NOT pay or hols!
My last interview I had a question I literally couldn't answer - tell us about when you did xxx - which they knew from my cv I hadn't done - so I said so, and then tried to say what I would have done... I got the job!
Are you chatty and bright? I am (well, chatty!!) and friends advised toning that down as it's scary. Otoh if you are quiet make sure you push yourself to sell yourself, even if it's not your normal style. Good luck!