I'm not an AdWords customer, but I
am a web publisher who uses AdSense. So I don't like to see badly-targeted advertising campaigns because they reduce the chance of my visitors finding the advertising relevant.
Below are a couple of tips that I think will help you to avoid preaching to the uninterested.
I have a page about a piece of software called Blender on my site. Blender is a 3D graphics modelling and rendering tool, so the keyword modelling appears quite frequently on the page. Unfortunately this means that the AdSense banners for that page display adverts for photo-shoot modelling, modelling agencies, and kitchen food blenders. People who have specifically chosen to visit a page about a piece of graphics software are probably not looking to buy a food blender and are very unlikely to be even remotely interested in photo-shoots for modelling agencies, so these ads are dead space. This is especially bad news for the advertiser if they're paying CPM rates.
Luckily, the AdWords system offers several keyword matching options to help you target your ad campaign more precisely to search queries. According to the video tutorial How do search & content placement work?, the negative keyword matching option allows you to avoid your ad appearing on unsuitable web pages. To avoid your modelling agency ad appearing on my page about 3D modelling software, you could try to combine the keyword modelling with -3d and -graphics. This should let the AdWords system know that your advert should not appear on pages about computer graphics. The AdWords Learning Center has a section about Keyword Matching Options which includes examples of using negative keyword matching to reduce unwanted page impressions.
Another example is my page about Sutton in London. Unfortunately for advertisers, there are a huge number of places in the UK called Sutton, so the page often displays ads about a different place with the same name. For instance, my page about Sutton in London often features ads for hotels in Sutton Coldfield — which is in Birmingham, not in London. In this case, you ought to be able to reduce unwanted impressions by using negative keyword matching such as -London and -Surrey. But there are so many Suttons in the world that you are probably better off just using a specific phrase match in the first place, such as "Sutton Coldfield" (the quote marks are important here as they turn the keyword into a phrase match rather than a broad match). This ought to stop your ad showing on pages that aren't relevant. Even though you will see fewer page impressions with more specific keyword matching, your CTR will almost certainly be higher because your ad is showing to fewer unsuitable viewers. And a higher CTR will cause your ad to be given a higher placing by AdWords because a high CTR gives your advert a higher Quality Score.
This is more for your benefit than mine. A couple of times I've clicked an AdSense advert about an electronic product, and I've ended up at an online store based in the US. I'm based in the UK, so ordering goods from the United States just doesn't make sense because of the huge cost of trans-Atlantic shipping. Which means your AdWords campaign has just cost you money (which is bad if you're bidding with a high CPC), and all you got for that expense was a visit from someone extremely unlikely to become a customer. Unless you sell items that don't have a high cost of shipping, advertising to people in distant continents probably isn't going to do you any favours. (To ship a couple of lightweight computer peripherals from the US to my home, I was recently quoted $135. That is not an order I can afford to go ahead with.)
When you create your AdWords campaign, think about who is unlikely to go ahead and place an order for your goods or services. Then use the geographic location targeting to only include countries that are a safe bet with respect to getting orders. As with using negative keyword matching, careful geographic targeting will reduce the number of page impressions your ad gets and possibly reduce the number of click-throughs you get per day. But because your ad will only be showing to more suitable visitors the CTR for the ad should go up, which will improve the Quality Score and the position that AdWords gives your ad. Best of all, when a targeted visitor does arrive at your site they're much more likely to be interested in placing an order than a distant visitor. So your return on advertising investment will be higher. And I won't be exasperated to find I've just followed a link to a retailer located more than five-and-a-half-thousand kilometres away.