Secret #1: Split Up Your Campaigns & Ad Groups Secret #2: Create Extremely Specific Ads, Match Your Ads to Your Terms Secret #3: Use Your Keyword In Your Ad (sometimes) Secret #4: Create Multiple Ads & Monitor Those Ads Secret #5: Stay Up-To-Date, Use Google's Help Resources
A general tip I find useful - Slice and Dice on every dimension which AdWords lets you do so: 1. Search terms - use negatives (most useful - negative phrase) 2. Geo targeting - consider removing under-performing regions, or geo-splitting the campaign - separate bids for the best geo locations 3. Content/Display - pass converting placements from "Automatic" to "Managed" and remove the under-perfoming 4. Time of day, weekday etc. Generally I take actions only for the elements with statistically significant conversion rate, using "binomdist" and other Excel functions to approximate the P-value. If your Revenue/Conversion has a wide range of values then the calculation is more complex.