The abundance of monsters that got "Improved Grab" as an ability was probably one of the reasons why we knew the rules pretty well (though there were always corner cases we couldn't find satisfying answers for), and we also learned the defenses against it. We mostly relied on magic - Freedom of Movement, Dimension Door, Teleport are probably the best ways to escape, and since they can be cast from Scroll, it's a lot easier to have them around then forcing characters to take feats to negate grapple attempts. But these are also an option.I made a house rule making it easier for players to escape grapples (don't add in the defender's BAB on grapple checks), but I still haven't solved the problem of monsters that Improved Grab and constrict people to death. This is almost the only way I've ever seen a character die in my year of D&D -- to owlbears, to giant bears, to scorpions, and (nearly) giant crabs and rocs.
It's not the grapple checks. It's the fact that Improved Grab cuts off the possibility of retreat. You escape, you five-foot step, they hit you next round and grab you again. You escape and run, you get AoO'd and they grab you again. You can't do anything else either like drink a potion of gaseous form. You're just screwed, it seems like. What do you do about improved grab? Scout and only fight at range?
Well, you can get Dimension Hop at level 1.Solutions that don't work for me: I have never seen a party with access to Dimension Door or Freedom of Movement, even once much less regularly. D&D is low level most of the time for us.
CMB = BAB + STR + positive SIZE modifier
CMB = 1/2*BAB + STR + positive SIZE modifier
Combat Maneuver DC = 15 + CMB
Combat Maneuver DC = 10 + CMB

(Dungeons & Dragons)
Rulebook featuring "high magic" options, including a host of new spells.