I used to have problems with intensity on my coasters, but I've built so many now, that it is very rare that I build a coaster that's over 10 intensity, even on the first run. I just know what sort of things to avoid.
For instance, never make non-banked turns when going faster than about 25 mph. large, non-banked inclined turns can be taken at about 35-40 mph, as long as there's not too many. Avoid corkscrews at anything over about 40mph entering it. Avoid small loops at anything over about 45 mph, and large loops at around 55-60 mph. You'll have to get a feel for the speeds, and it takes a while.
One thing to do if your coaster is too intense: Look at the max vertical, negative, and lateral Gs. The peeps can handle fairly strong vertical Gs if they're not sustained, but try to keep the max below 5.5. Avoid having negative Gs greater than 2, and try to keep lateral Gs below two as well (although sometimes 2.5 is ok). If you're coaster is too intense, look for the parts of the ride where these Gs peak (look at the data recorder), then modify that section to reduce the forces there. If you do this, you can build large, very exciting, not too intense coasters. I've built 9500 foot long hypers (240 foot drop) with no trims at all, with an excitement of over 10, and an intensity of 9.85 or so. I've also managed a large floorless with 8 inversions below 10. (I've done more inversions without bad intensity, but they're always small, and they crawl through the elements). Good luck!
Jman