You don't usually need to do anything special to prepare for an X-ray. You can eat and drink as normal beforehand and can continue taking your usual medications. It's a good idea to wear loose comfortable clothes, as you may be able to wear these during the X-ray. Try to avoid wearing jewellery and clothes containing metal (such as zips), as these will need to be removed.
For all X-rays, you should let us know if you're pregnant. X-rays aren't usually recommended for pregnant women unless it's an emergency.