My main suggestion is experiment. Test, exercise for 20 mins, test again. See what your blood sugar did, if anything. From there, make adjustments to temp basals or what you eat before exercise.

Personally, temp basals have helped me immensely when I exercise. My blood sugar tends to go high when I lift and low when I do cardio. Example of a personal experiment: I learned that if I have a heavy legs lifting day, my blood sugar can go from 86 to 300 in 30 mins. Solution? After trial and error, a +90% temp basal for an hour will bring me out under 140.

I actually never had much experience with temp basals and found that most of my BG problems came well after a workout. If I used a temp basal, I usually just ended up high!

I rarely needed to adjust right before working out, unless I was edging toward a low. If I was 150+ I could exercise and drop without an issue. If I was under, then I would eat a very small snack, sometimes just drink a glass of milk to bring myself up a bit and then would come back down from the exercise increasing my glucose uptake. I would also adjust my post-exercise meal if I ended too low.

I really watch and adjust on a case by case basis. As you can imagine, no day is ever the same so I never start exercising at the same number. I sort of have "contingency plans" so to speak. I definitely recommend keeping a log of everything you do and you'll start to see what works best for certain conditions and what you might need to do to prevent a high or low. My biggest advice is don't be afraid to eat before or after a workout to manage your diabetes. Most of the time you need to eat a small snack anyway, so you can just build this into your normal fueling for the day. It can feel like you're "eating the gym" but you have to eat calories during the day anyway, so try to time your workouts near a meal or snack. You're not eating extra, you're just eating smart.