You can take the following points as guidelines when bidding
1) Always target the location where you are providing services or products.
2) Even if you want to target keywords on multiple countries create them in separate ad group in that way you would be normally paying less.
3) Google provides first page estimate CPC, always try to add one to five cents to that CPC and bid.
4) You should make sure if the keyword completion decreases for keyword you should go and reduce your bid. This you should be checking regularly for all the keywords.
5) I would suggest not to display ads on content network, but I will leave it up to you.