Staining doors when they're attached to cabinets isn't just more difficult; it can also lead to unwanted and unsightly drips and bubbles. So, the first step in how to stain kitchen cabinets is to remove all the doors, as well as the hardware. Use a small piece of painter's tape on the door backs to label their placement; use small zip-top bags to identify hardware. Then, lay your doors flat in a vented area on top of a large drop cloth.
In order to enable the new finish to properly adhere to and protect your kitchen cabinets, you'll need to remove the original finish. To do that, you need to sand the kitchen cabinets, either by hand or with an electric-powered hand sander. Start with a heavier grit—about 100- or 120-grit sandpaper—for the first pass and sand with the grain. Wipe clean, then sand with a finer grit, such as 180 or 220. Wipe clean and apply a wood conditioner with a clean rag.
If you are also changing the stain color of the kitchen cabinet frames, you will need to repeat this process with the frames, too. If there are large areas of the cabinets to refinish, you might want to take down the cabinets to work on them more easily.
Finally, you'll begin applying the new finish; generally, many people choose a stain/polyurethane combination in order to color and seal at once. Apply one coat, then follow the manufacturer's directions for dry time. Apply a second coat and let dry, and apply a third coat if needed. Once fully dry, reattach the hardware, then rehang the doors.