I am trying Adwords for my web hosting service and some lessons learnt:
* Try long tail keywords for competitive niche. The per click cost is less and the sale conversion can be higher.
* Observe other top performing ads and refine your ad copy. The copy needs to be relevant for the keyword. Same copy doesn’t trigger your ad for all keywords.
* Even if it is a global niche, try targeting audience in your locality. People may be comfortable buying from a local guy. You can also switch off the ads during night time in your region.