IMHO, there are a few things the Dems could have done to keep the House in 2010:
1) pass bigger stimulus in 2009: as Many liberal economists, especially Paul Krugman and Joseph Stiglitz, were urging Obama to go bigger than he did in 2009. After all, in constant dollars, Obama's stimulus may have been smaller than FDR's New Deal public works programs and Reagan's 1981 tax cuts. The Obama Administration was concerned about the deficit, but in reality, do the voters really care about the deficit? It's an abstract number to most of them. I think voters really care about unemployment and inflation, which are matters that effect them directly. And to go back to 2 names I brought up earlier, FDR and Reagan both used deficit spending to stimulate their economic recoveries, and neither of them were hurt politically, and in fact, just the opposite. Both of them were re-elected by historic margins. A bigger stimulus likely means a much stronger recovery by the time the 2010 midterms occur, thus giving the Democrats a much stronger platform to run on.
2) Keep public option portion of Obamacare: I think this is crucial. Both Obama and Pelosi caved in way too quickly on this issue. The public backlash against Obamacare was (and is) the private insurance mandate (a conservative idea). Keeping the public option in demonstrates to the voters that they are not tools of the insurance companies. Furthermore, they should have done a much better job of communicating to the public that the insurance mandate was in fact initially a conservative idea designed to keep private insurance, rather than the government, the main provider of health insurance. I could go a step further and suggest that the Democrats should have from the beginning pushed for Medicare for all and let the Republicans negotiate down from that, but I'm probably being a little bit unrealistic there.
These next two are most likely ASB, but I'm going to throw them out there anyway:
3) a huge oil glut in Obama's first term: this is important because I think both the Reagan and Clinton economic booms were fueled largely (but not entirely) by the cheap gas prices of the 80s and 90s. We are having a bit of an oil glut now, and I do remember there being a plunge in oil prices early on in Obama's first term, but it didn't last long. But I think a long and significant plunge in oil prices would have definitely politically benefited the economy, and the Democrats, considerably. But, I do think this is likely ASB as there really is not much the President can do to directly effect oil prices, especially in the 2 years between Obama's inauguration and the 2010 midterms. But if by some miracle this did happen, then the Democrats probably fair much better in 2010 (especially if this occurs along with the other 2 events I mentioned).
4) catching Bin Laden shortly before, rather than after the midterms: again, probably ASB as I don't know all the details and events leading up to Bin Laden's capture and whether anything could have been done to speed up the process. Plus, if Bin Laden is caught around the time of the mid-terms, there are definitely going to be screams from the opposition that this was staged as an "October Surprise." And admittedly, the timing would seem a little suspicious (or at least portrayed as such). So this part is a bit iffy.
So there you go. If the above 4 events happen prior to the mid-terms (and I do once again acknowledge that the last 2 events are likely beyond the control of Obama or the U.S. government in general), then the Dems likely hold on to the House in 2010, and possibly increase their control (not a strong possibility as the only time I think this has happened before is 1934).