The standard for a Democrat is to run to the left, although it'll be tough to outflank Marianne Williamson on the left. The one candidate who looks to run as far to the left as she can is Wendy Greuel. She has an ad out where she's doing just that.
This ad could work for her because there are a lot of "good progressives" in CA-33, but the ad is so bland that it reminds me of her really awful campaign for mayor in 2013.
There are five major, and a bunch of minor, candidates going for the left leaning vote. There is only one candidate, Republican Elan Carr, putting money behind the Republican vote. If you divide the Democratic vote five ways, you won't get a lot of votes. You could divide the Republican vote in three and you still might be larger. In 2012, there weren't many districts where Democrats were able to get Republican votes in the primary, but it happen. Here's Ted Lieu's ad.
Lieu's looks like he's running to the middle, as he goes with an issue, NSA spying, that crosses party lines. Yet he threw in that he was endorsed by the Democratic party. If you want NPP and Republicans to vote for you, you don't include that. You put that in mailers and phone calls specifically hitting Democrats.
Matt Miller's ad seems more centrist. He's definitely trying to go after the "no label independent" crowd. He mentions working for Clinton, but doesn't use the word "Democratic." People like Clinton.
David Kanuth doesn't seem to be running on anything but nice people like him. He even has a Democrat and a Republican in his ad. It's an okay introductory ad, but he'll need to give more if he wants people to vote for him. After all, his opponents have records to run on.