When you’re in your Adwords account looking for something to work on, make sure you have sorted by a column that is going to give you your most profitable/highest converting campaign/ad/keyword at the top of the list. These are the ones you should be spending your most time on optimizing. They are making you the most money.
By the same token, also sort by a column that will show you your biggest spenders at the top; the ad, keyword or campaign that has cost you the most money. Go through the top 10%-20% of your most expensive items. Look for any leaks, items that are costing more than the rest and bringing in less revenue. Modify these or turn them off.