The Right Combo

Summary: Mathematically BAM (Barb, Arch, Minion) is the most efficient combo for farming once properly used.

Explanation: BAM is efficient because it gets 6 barracks working for you instead of 4. The barbs are necessary for a little tanking and the archers for buildings behind walls. A 50% increase in production capacity only means you can spend more time farming and less time waiting. While it's possible to get good farming results with other combos, over time BAM should produce better results just because you are making more troops faster.

Goblin usage may get similar results since you can skip buffer buildings and go straight for mines, but I haven't spent the time to do a comparison.

Right Base that you try to attack.

Summary: Picking the right base is probably more important than what combo you use or how much gold is available for fast efficient farming. Learn the signs.

This is the most important part of increasing your efficiency because picking the wrong base can set you back in time, cups and troops. When analyzing the defense, try to get used to thinking about how many troops you may need to use to get the gold easily. A 200k or less base that requires all my troops to get it all is an instant skip for me. Refer to the Math section for the GPU you want to target.

• Gold Available - obviously the first thing to look at while spamming next. I generally only start scanning a base if it's over 100k. This can give you some clues on how much is in pumps however. This is why I generally skip TH10s as a TH9 because even with 300k showing means most likely there is only 60k in the pumps. TH10 I'd need to see over 360k or if it was prem to considering going for it.
• Gold Storages - I do a quick scan to see if the gold storages are full. If they aren't empty I skip unless the loot is over 300k or the storages are easy to get to. The graphics for the gold storage are bugged however so an empty looking storage is not enough info to press go.
• Mine Positions - if the gold available is good I scan to see if the mines are on the outside or first wall layer. Some bad bases randomly sprinkle mines further into the core. I will probably skip these unless the loot available is high and worth the extra troops it will take to get there.
• Even Resource Amounts - Even numbers in the mines like 75000 or 150000 are a good sign they are maxed.[thx dahimi and siv75]
• Similar Resource Amounts - Resources close together like 190k gold and 190k elixir. [thx dahimi]
• Elixir Pump Levels - I didn't know this got fixed, but they show graphically now whether they are full or not, a good indicator of possible mine levels too. [thx siv75]
• DE Drills - once I've decided the mine positions are good I look for DE drills. These are one of the few reliable ways to see if the base is abandoned. If the little square box on top is full it's a good chance so are the mines.
• Tombstones - if the DE drills weren't conclusive I scan for tombstones to see if the base is inactive and has been raided. I often skip a base if I see no tombstones even if the other signs were looking good.
• Workers - Some bases can fool you having all the above look ok. But if you see multiple buildings being upgraded there's a good chance the loot was all in the storages and the player is purposefully not collecting tombstones.

It takes some practice to run through all these but it will become second nature for a seasoned farmer.