Here are some things I've picked up.
Water for the boil should have alkalinity below 50 ppm. The need for adjustment depends on your water. Bru'n Water can help figure how much acid to use.
CaCl and gypsum might help, depending on your water and the extract manufacturer's mash water chemistry. Making up dilute solutions and adding to a glass of beer can help you decide whether, and how much, to add.
DMS: It doesn't seem to be a problem. I've never had a problem with it, even when doing covered hop stands.
Adding LME: Late extract addition has become popular. I add enough extract at the beginning to get about 1.040 SG in the boil. Then add the rest at flameout. Also, make sure the kettle bottom won't scorch the extract - I wait one minute after taking it off the burner before adding extract.
I've gone to a 40 minute boil. This seems to be getting popular.