When you do the advanced scouts at the beginning of a new chapter, that helps to make things significantly easier. Also, if you do all the squad upgrades, that makes it easier too, but only for the territories you have not yet scouted. The ones you've already opened (but not completed) will remain at the same level.
The best way to insure that you don't have too many hard ones is to not overscout. Check the next chapter (for example, if you are in chapter 5, check the opening tech for the next chapter). See how many provinces it takes to open the next chapter. If you are already way past that number, then you've overscouted. If you are close to it or just past it, then you probably aren't overscouted, but in the early chapters, it's easy to get into the "hard" stages. Make sure you do all the optional squad techs.