This isn't an area I think most of the current headliners are deliberately failing in. I think the writing team have become too used to having a select group of guys win most of the time. With the possible exception of Cena I think all of WWE's big stars would be happy to do their bit in this regard.
Apart from Ryback, and his credentials are questionable, every full time main event wrestler (which, for clarity, I consider to be Cena, Punk, Orton, Sheamus, Big Show, and ADR) has faced every other full time main event wrestler. It's true that reversing the heel-face roles for some of these feuds would freshen them up a bit, but that's only a short term solution. Turning someone doesn't completely overhaul their wrestling style and it only partially addresses the problem of stale characters.
The best thing WWE could do is select three or four guys and begin elevating them immediately after WrestleMania. Putting them into feuds with bigger stars and granting them clean, decisive victories would go a long way towards portraying them as the equals, rather than the inferiors, of the top boys. Ideally they'd all be given high profile programmes and sustained pushes across the summer, with the plan being to give each of the chosen ones something especially memorable to do at SummerSlam. Getting a world title or winning a particularly gruelling gimmick match, for example. That would also bolster SummerSlam’s rep as an important show. It's flagged badly in recent years.
Obviously Dolph Ziggler should top the list of new pushes. It seems likely he's going to leave WrestleMania XXIX as the World Heavyweight champion. There aren't many better ways to move someone up the bill than that.
Jack Swagger's a possible candidate but truthfully I think he's better cut out for the mid-card for now. He's solid in the ring and his recent character overhaul has worked out well but nothing about him stands out as headline calibre. He could benefit from 'The Show Off's' push though. As he's already involved in a WHC programme with ADR a three-way match at Extreme Rules is easy to imagine. That match would have the added bonus of having a heavily stocked ringside area. It could be great.
Cody Rhodes, Damien Sandow and Wade Barrett would all make good choices for a proper move upward too. Personally I'd select Barrett. I think Rhodes and Sandow are of more use as the Rhodes Scholars. All three are good enough to be placed into ongoing, pay-per-view rivalries with the big names. Sheamus would be an ideal opponent for any of them: he's wrestled good matches opposite opposite each one on TV but hasn't wrestled any in a major PPV bout.
WWE needs babyfaces too, of course. I'd love to suggest Zack Ryder, but he's been stuck doing so little for so long that a sudden leap to tangling with CM Punk on pay-per-view would stretch credibility too far. He would be an ideal candidate to be moved up into a vacated mid-card spot though.
Miz isn't a particularly strong candidate either. I'm more partial to his face turn than a lot of other people but I don't think he's due a return to the top any time soon. His niche is the upper mid-card.
A better option would be Kofi Kingston. WWE have faltered over pushing him in the past, but the fact they've started so often shows they see something in him. In fairness he's not quite a good enough promo to be a success in a promotion like WWE. They want their top guys to have it all.
That problem could be overcome though. Ask The Rock to spend an afternoon or two with him while he's still making regular appearances. Better yet, have 'The Great One' give a talk to the entire roster about connecting with an audience. He's one of the best ever at that. Everyone could learn something from him.
The best new good guy WWE could go with is Daniel Bryan. 'The World's Toughest Vegan' has more experience than many of the promotion's existing stars, is one of the best wrestlers in the roster, and is a reliable promo. His character would need some tweaking because the whole yes and no thing is becoming played out, and because it's not something WWE are going to get behind with a headliner.
Establish Bryan as a face, separate him from Kane, either after a feud or an amicable split, and give him some wins over main eventers not named CM Punk on pay-per-view. If treated right he could be massive. In fact I’d go so far as to say that if he were booked correctly over the next year he could challenge Undertaker's Streak at WrestleMania XXX.
They key to getting this proposal to work would be sticking with the pushes and ensuring that each rising star was treated as an equal by whoever they were pitted against. The WrestleMania to SummerSlam stretch is a big enough gap to fit in two feuds for each guy. Plan out who's facing who, who's getting victories when, and stick to it all.
Most importantly, keep Cena away from the process. He's a liability and doesn't seem to understand how to make others look good. Worryingly he hasn't ever displayed any understanding of why he should, either.
The success of Santino at last year's SmackDown Elimination Chamber match shows that with the right booking anyone can become a serious star in WWE. Fans went wild for 'The Milan Miracle's' short battle with World champion Daniel Bryan. They genuinely believed that Santino could dethrone the champ, and they wanted to see it happen. If that can happen with a low card comedy act like Santino (who was a last minute replacement in that match, not the recipient of a long term push designed to make him a bigger name) then WWE can make anyone a star.