Your search marketing campaign is not a set it and forget it effort. To be effective, pay per click search marketing requires continual attention. Here are a few things you should be doing on a regular basis:

1. Test your keywords. You should be constantly testing keywords and keyword phrases. Aim for a click-through rate around 4%.
2. Aim for the most cost effective ad position. Paying for top placement isn't always necessary. You may get great click-throughs when you appear as the third or fourth ad. Test your placement and adjust your bids as necessary.
3. Split test your landing pages. Test your headlines, your copy, your button placement, your call to action. Everything and anything. You'll be amazed at what leads to higher conversions.
4. Update your landing pages. As you adjust your keywords, your landing pages will need to be updated in order to maintain a good quality score. Aim for a conversion rate of at least 4%.
5. Optimize your ad. If you're not converting at least 4%, your copy is probably misleading in some way. Are you attracting freebie seekers? Were your visitors looking for a different brand? Review you ad with an objective, critical eye.
6. Maintain adequate stock. While this may not have anything to do with the effectiveness of your search marketing, it seems useless to pay for visitors who can't buy what they came for anyway. If you know an item is a hot seller, be sure to pause that ad group before your inventory runs out.

Time to implement: Maintaining an effective search marketing campaign can be time consuming - it all depends on the size of your website, the number of your ad groups, the amount of your keywords and the size of your budget. In my experience, a mid-sized campaign with a $300-$500 monthly budget requires approximately 2-3 hours per week for testing and updating.