As already said, clean and cut as you would normally, to whatever size you would want later.
Instead of packing them into a bag, scatter them on a flat surface (cookie sheet, tupperware box, etc.) until frozen. Then transfer to a ziplock bag. This way makes it so you can bring out only what you need, rather than having a frozen clump!
Then just add directly to whatever you are cooking. No need to thaw.
Do the same with onions and celery, and you have ingredients ready for a stir fry, soup, casseroles, etc. without a lot of work at the time!
Bon Appetit!
