How do I set a initial condition for repeat?

From the manual:

Simply repeat the event a given number of times. This tests any conditions following it on every repeat, and if those conditions are met also runs the actions and any sub-events on every repeat.

How can I make a condition that will be checked once before the loop and start repeating if that condition is true?

The order of conditions in an event is important. This will check the condition once, and if it's true, repeat the loop 10 times:

Condition
Repeat 10 times

Repeat 10 times
Condition

Repeat 10 times
... // sub-event
... Condition

Til, after 10 years of obsessively refactoring event counts down, thanks for this tip lol. I might have even made some mistakes if I thought all condition was being checked every iteration regardless of order hmm....

Although the sub event method is often useful for running actions at only the start or end of a loop.

oosyrag haha, I too still learning basic things about Construct. A few weeks ago someone told me that the default order of instances is based on their zIndex, not on their UID or the order they were added to the layout. I always thought that an instance with IID=0 is the instance with the lowest UID. (facepalm)

By the way, the order of conditions is especially important when using "For each" loops. I prefer picking the instances first, then iterating them, I believe it's better for performance:

Enemy is on screen
Enemy is overlapping Zone
For Each Enemy 
......