According to a study from online-ad-research group Dynamic Logic

After analyzing more than 170,000 online ads, the Millward Brown company determined that creative factors such as persistent branding, strong calls to action and even human faces make for better ad recall, brand awareness and purchase intent.

"If people think of the internet as a well-targeted magazine and do their planning and creative development around that, they tend to have very successful campaigns."

it's smart to use a logo -- a lot. Ads that leave the brand punchline until the very end of a bit of Flash animation largely don't work, so the report stresses that online ads need to be simple, direct and communicate meaning -- as well as the brand -- at a glance.

A few recommendations:

Highlight the brand prominently throughout the ad. "Intrigue is rarely a good strategy in online campaigns," the report says. Ads with omnipresent logos had the highest brand and online ad awareness.

Make each second count. Whether it's brand awareness or a call to action, the ad should support the message at all times. The ad will probably only get one second with the user, so each one counts.

"Reveal" ads don't work. Get right to the point, because you can't expect the user to wait around and watch the ad in its entirety. While this applies to all industries, for CPG ads, 1 out of 20 top performers on ad awareness used the reveal format, while 17 out of 20 bottom performers did. Dynamic Logic does cite video and highly entertaining ads as sometimes being exceptions to this rule.

Stay simple. Dynamic Logic recommends using no more than two messages per execution. For example, copy-heavy ads for financial services advertisers tended to underperform on awareness.

Use people. People imagery was found to work especially well for financial services campaigns.

Note: I'll add one more from my own harvest: (without any real metric to valiadte it)

If you have a strong campaign that is very creative and is sucessful, stick to the strong concept that is consistent with the overall campaign.