I will give a correction dose when I think I'm too high. That's not a very scientific answer is it?
So everyone will have their own target range. When I exceed the upper limit of my target I will think about giving a correction dose. But before I do I will also think about why am I so high? Is it because I didn't carb count very well for my last meal? If so I would lean towards correcting. Is it because I'm ill or in pain? Again, if so, I would lean towards correcting. Is it because I'm stressed? If so I would be much more cautious about correcting because I know as soon as the stress goes I'm likely to drop.
I would then also try to think about whether I'm too high because I'm peaking (& therefore likely to be on my way down again anyway without a correction dose) or if I have plateaued at a level higher than where I want to be. To work that out I have to think about how long ago I ate and how fast acting the carbs I ate were and how long ago I injected. If my last injection was less than three hours ago (some people work on 5), I know that insulin will still be working so I'm less likely to correct.
If I do a correction dose it's sensible to keep a close eye on what that does to my blood sugar after (you can see there's quite a lot of variables to consider). And also remember for the next meal that you might still have the correction dose working so you need to factor that in when taking your next bolus to avoid insulin stacking.