According to Gallup's table, the only State of the Union that had a really significant impact on a president's approval ratings was Bill Clinton's 1998 address, which lifted his favorables from 59 percent to 69 percent. And looking at approval numbers for that year, it looks like that benefit stuck with Clinton for a bit. So how'd he do it?In fact, what happened between Gallup polls that year was not just Clinton's SOTU, but also the first news of the Monica Lewinsky scandal, which dominated the news in the week ending with the speech. Fortunately, we know a lot about this because there's a great article about it by the political scientist John Zaller, "Monica Lewinsky's Contribution to Political Science" (speaking of how to title your academic papers...; link is gated, but look around and you'll find it).
What Zaller finds is that the initial news of the (at that point alleged) affair hurt Clinton's approval ratings for two days, during which time the news was totally negative, but after that, as Clinton fought back and the news became balanced, his approval ratings bounced back to a higher level than they had been initially. His hypothesis is that, basically, the new higher ratings reflected peace, prosperity, and policy moderation. The main effect of the scandal in that first week, he speculates, was to force people to drop their standing decision on the president and re-evaluate it in the current circumstances and they liked what they saw. It's a great essay, and I recommend the whole thing.
At any rate, getting back to the question of "how'd he do it?" -- the answer is almost certainly not about the speech, but about the Lewinsky scandal (one note: the dates in Gallup's table today don't seem to correspond exactly with the dates in Zaller's paper, but since he uses polls by multiple organizations, I don't think it matters much). So while I recommend watching it anyway for those who want to see a real master of that particular setting -- Clinton was better at delivering joint sessions than, I think, any other president in the television age -- it's not going to tell you much about what Barack Obama should do tonight.
(Ronald Reagan was probably second-best during the TV age at addressing joint sessions of Congress, but I think he never found a way to get the setting to enhance his style; his best performances were elsewhere).