Turning the keyboard upside down invariably dislodges some of the debris but not all. Some people go to extreme lengths and prise off each key, not something I would personally recommend, especially when you consider that some keys are held fast with metal pins. The best advice is to clean the keyboard using compressed air. Its long, thin straw-like attachment can easily slip in between the keys and dislodge almost anything. Spruce up the mouse.
Debris gathers underneath as the mouse slides over surfaces.
If the mouse seems to be sticking, then it may well need cleaning, which is a simple enough task to do. Wipe over the top of the mouse as you did with the keys on the keyboard. Then clean the bottom of the mouse with a dampened rag. To remove the ball, gently manipulate it free from its casing. Using cotton swabs dipped in rubbing alcohol, carefully clean the metal rollers inside the mouse.