Here are following tips for Adowrds Beginner:

Begin with a value like $0.25 as max bid.

lets assume that this will lead to an average bid of $0.20 (not all clicks will cost $0.25) and you have a conversion rate of 3% (% of clickers that buy from your site:

so you will spend 0.20/3% = $6,7 - its ok for you spend $6,7 per product that you sell?

So this are the numbers, you can by the time measure and adjust the conversion %