My grandma (type II) really liked her water aerobics class and was able to loose 100lbs in a year via aerobics and dieting. But I think she only had a once a day treatment and I know she's never needed insulin. I think it depends on how bad your diabetes is- is your blood sugar hard to control? I would recommend starting slow, like walking. Make sure carefully watch your sugar levels (before and after) to see how your chosen exercise effect it. Also if you plan on going to a gym or far from home, make sure you have emergency pills and maybe even glucose syrup/candies on you- just in case. If you start feeling dizzy, confused, or start shaking make sure you stop! It's good to push yourself but not at to the point where it could be dangerous.
And remember -exercise alone won't do very much. Make sure you're adding a good, balanced (and of course diabetic friendly) diet. Good luck!
Any exercise can lower blood sugar, but how much, depends on how high your blood sugar is, and the intensity of the exercise, along with what you ate just before.
Ducky is right - you have to watch your food intake, opting for low glycemic foods (those that don't raise your blood sugar quickly). These will lots of veggies (both cooked and raw), lean protein, fiber, "good" fats, etc.
Do you have Type II diabetes? What medication are you on? The time(s) for taking them can vary depending the medications and how many times/day you have to take them...
Working out is a double edge sward for some it will lower your BG levels for other's it will make them go higher - and it all depends on how the body reacts to what is going on.
I can hit the gym for 4 hours and my levels will go down hit it for an hour and they pike like crazy, yet I can set up a photography studio kit in 30 minutes and my levels will bottom out - as in I'll be at mmol 10 (180) before starting to set up and by time I'm finished setting up I'll be hitting mmol 3.5 (63) all because of how putting the equipment together can be (hefting and hauling 150 pounds worth of photo equipment uses a lot of glucose).
I would suggest that you take readings before working out and after and chart them to learn how your body does - record what you where doing and for how long, you will eventually get a picture as to how it effects you.
As to taking medication, that one is best left up to your doctor to say.
As an RN and diabetic I agree with what Nyxks said about checking ur glucose before and after and writing it down to get a good picture of ur levels. Meds should be taken 30 min before meals. Low impact exercise is best until u get a good idea how ur body reacts. As always, consult ur doctor about what's best for ur situation.