If your type1 diabetic you shouldnt try to lower blood sugar too quickly as the large fluctuations can cause mood changes and cravings making you want to eat and so continuing the "out of control" cycle.
Doing some exercise can help to burn off the extra sugars in the blood. Type 1's with high blood sugars, can also try to reduce their blood sugars by giving themselves one or two extra units of their fast acting insulin on top of their normal dose and not take anything extra outside of this because high doses of insulin can make you hungry. Just do it gradually.
It is important to drink more water when your blood sugars are high.
I've been insulin dependant for 25 years and would be very interested to learn if this is the wrong advice to give so please feel free to correct me.
If you have Type 2 diabetes, sometimes a healthy snack before bed tricks the liver into NOT making as much sugar. A few slices of apples and a few cubes of cheese could help. The fat in the cheese slows the absorption of the carb.