Zhure has some great advice, almost the Commandments of being a sorcerer. One thing you might want to see if your DM allows is upgrading your spells. There was an option in some dragon magazine, basically it lets you swap up lower spells for better versions when you learn the slot, if the new one reffers to the old spell. For example if you knew Invisibility, a second level spell, when your sorcerer hit 8th level and got a 4th level spell slot you could choose Improved Invisibility, and replace Invisibility with a new 2nd level spell. You can do this with any spell that reffers to an earlier version, Hold Monster is a usefull one, it says "As Hold Person."
For spells, Limited Wish is a must to get your available spells up. You might alsowant to look at Shadow Conjuration and Shadow Evocation, prefferably the greater versions. These also greatly increase your effective spell use.
Someone mentioned Maximize spell, but i would say stay away from Maximize Spell. Empower spell is often just as good, adding 1/2 again damage for one spell level lesser. By that i mean an Empowered 4th level spell costs the same slot as a Maximized 3rd level spell, a 6th level slot for both, but the Empowered 4th level will have higher damage and a higher DC most of the time. Plus, you can use Empower 2, or even 3 times for mega damage. Applying both would be nice, but sorcerers don't have the feats to throw away on both.
Spell Penetration, well i've heard its one of the best feats from players who play high level. We've never played the levels where it would be usefull, so i'm not sure. I'd wait till you get to those levels and see how many things are resisting your spells.