Romney is hard to sell, because there isn't much good about him. Also, the way I would attempt to sell him wouldn't be how his political handlers do. I am a liberal, but I will do my best to make a mock campaign strategy.
1) Bain business experience. I would tell Romney to focus on his experience as a CEO. He could claim he reached the highest position in the private sector, and it was not by accident. It gave him understanding in what companies need to be successful.
2) Massachusetts Governor. He could claim he was elected as a Republican, and still was able to govern without gridlock. This shows he can reach across the aisle. Throw in the Olympics here also.
3) Moderate (I wouldn't make him become a social bigot, but this also assumes he is past the primaries, which I am completely ignoring). Romney could say he was in favor of gay marriage and a woman's right to choose, along with curbing carbon emissions RESPONSIBLY, thereby bucking GOP orthodoxy, but showing independent voters he is not a partisan ideologue.
4) Being wealthy. He is a great position to explain just how much of a tax burden the rich have to pay. He could use his tax returns as an example of everything that is wrong with America, and call for lower taxes on ALL. His budget plan would need to be framed as creating private sector opportunities, rather than firing government employees (he may be susceptible to attacks here because of his gaffe about liking to fire people).
5) Social work. Romney should highlight any kind of charity work he did while on his Mormon mission, along with anything done recently (this would be done by operatives, not Romney himself, to avoid looking conceited).
Take it for what it's worth, which may not be much!