Ensure that you have a clear, well ventilated and dust-free workspace. If you are painting MDF furniture that has already been made up, you can disassemble it and paint each piece separately or paint the piece of furniture as is. If you are going to paint your already-built furniture, and if possible, elevate the furniture so that you can paint it quickly and avoid messy bottom edges.
For built-in furniture, you may have some small gaps between the furniture and the wall; use caulk to fill in these gaps so that it looks neat. If you're painting built-in furniture on top of carpet or hardwood floors, try to place your masking tape under the furniture to avoid paint leakage onto it.
You can seal MDF edges with preparation tape. Due to the way MDF is made, exposed edges tend to absorb paint much more than the surface, so you will need to apply an extra coat or two of water-based primer on the edges. Preparation tape stops the paint from being absorbed by the MDF and acts as a primer, saving you time and effort.