If diplomacy is on, try to avoid sacking cities early on to protect your rating. Usually it's fairly save to sack cities starting turn 5 or so, this point also goes well with the above point for you may want to leave the strong cities for sacking.

Why would you want to protect your diplomacy rating? I'd much rather have 1000 gold in a couple turns and a second hero that much sooner. In the expansion phase it pays tremendously to have as many strike forces as possible going in as many directions as possible to occupy territory. Getting an extra hero early on - with allies - is usually a huge advantage.