Once you gain more and more experience in running campaigns, you might discover that bidding up is not so straightforward. Placing a high bid exposes your campaign to the traffic from more expensive targets, but the traffic volume you receive remains the same.

It might be caused by the fact, that targets have different layers of the traffic prices based on the operating system, browser, carrier, etc., and the available traffic that has not been brought onto the network.

Thus, it is best to rely on a win ratio of some particular targets and keywords in defining the best bid for your campaign.

If you see that you are still gaining the traffic as you are bidding up and your win ratio is growing, it indicates that you should go for bidding up. If your bid is high, you open up your campaign for more traffic that is currently unavailable to other advertisers.

Try to use short generic keywords as often as possible. For example, use credit cards rather than prepaid low apr credit cards or amazon vs. www.amazon.com/promotio.

Using broad match keywords exposes your campaigns to traffic that contains your selected keyword. For example, if you select auto insurance, you will also receive traffic from cheap auto insurance and auto insurance quotes.

Use word/URL variations, for example, car vs. auto; 

Search for popular misspellings such as credi cards;