1) Calibrate your monitor. Work in CMYK.
2) Ask for a color profile.
3) Ask for a calibrated softproof of a ploter print. This is their responsability to have calibrated.
4) An alternative is to send the colors in pantone. You probably should use a phisical pantone guide.
To clarify your comment.
A) A pantone guide is normally used phisically, because the one that has quality controll on the process, on how the colors look, is the phisical one.
Any digital one depends on aditional factors like monitor calibration, and active color profiles.
Of course a color can vary a lot depending on the substract where they are printed. On a pantone guide you could only have Uncoated or Coated. There are some specialized chips for textile and automotive paints, but in some other special cases, probably foil, you should talk with the manufacturer and see how the pantone colors vary once aplied.
One aditional thing is any varnish or plastic layers on top of the ink.
B) If the printer knows what he is doing and have a controlled method, they should generate a specific, and I mean a very specific profile for their process, they measure the theorical colors against how they are printed at the end, using their specific CMYK inks and considering the coatings and substract, and they could provide you the instructions to install it.
A generic one is for example, Fogra, Gracol, Swop, Eurocoated, but they are generic for paper.
A "Must" this days should be a calibrated plotter sample, so you can even send a patch of the desired color and some variations to choose later what is the correct one.
But I have seeing printers that make a Roll test, inclusive for metal cans... That should be a last test, not the initial one.