1. Create product targets as granularly as you can. Download your Google Merchant Center feed and add attributes per sku to the the AdWords_Label column. You should categorize for type, category, price, margin, style, sku and whatever else you can think of. If you can get all the way down to one product per adgroup, even better. There are two reasons for this: 1. the more specific you can be with your product targets the more specific you can be with your promo text which is set at the adgroup level, 2. you want your cpc bid to match as closely to the value of a click from that product as possible. If you have a very general product target then it will be hard to know what your bid should be when there is a wide range of products that match that target.
2. Use negative keywords to optimize your ads. You can’t bid on keywords with PLAs but you can see the queries that triggered your ads and add them as negatives (under the Auto Targets Tab > See Search Terms > All). Negative keywords are sometimes necessary to make distinctions between product variants. For example, if you sell a small and a big version of the same product you might want to add “small” and “little” as keyword negatives for the big version (and, conversely, add “large” and “big” for the smaller version).