Inside, well you should have an algae removal pad (pet store charged me all of .99 for it) or there are those fancy magnetic ones... Tho I'm much prefering my new way, chinese algae eaters, been in the tank for a week now, no signs of algae on the glass
Hungry little guys!
Outside, you can either blow the big bucks on the fishtank glass cleaner (wont hurt your fish like windex) or I just spray the windex onto a paper towel, and wipe things down, being very careful to stay away from areas windex might leak down into the tank.
Andy