***Since the last update this is not working but...***Alliance warfare is up and no good news for boosting sessions. Alliance wars don't give tags, only resources.
This will help going after Tags by finding easier targets. I found a way to go after lower level targets possible and that will help you get at least to 2000 Tags very fast. After that point you will need a more careful digging to find targets, but still possible as I unlocked the achievement while my command bunker at level 6.
When you get to 2000+ tags you will have to fight people of higher levels. You will get a lot of money for upgrades. But don't neglect building your defenses as you will also be targeted by high level players. So if you have your storage full don't attack another player until you spend your money. You will need it to upgrade. I bought the 3rd engineer (500 gold) to make upgrades faster. This is my defense setup (I actually unlocked the achievement when I got back and found 28 extra tags from defenses):
Now for the Tags. I found that by going to battle I was only finding people with higher levels than me with some only a few levels lower. Then I decided to check if Alliances were any helpful. And in fact I found they are.
To find your low level target:
1 - Press
and the select "Alliance"
2 - Select "Leaderboard"
3 - Scroll down to find a good alliance to go after, the lower the score easier to find a good target
4 - Press
to see people inside the alliance
5 - Scroll down to find someone with a low level, I recommend level 2, 3 and 4 until you get to 2000 tags. Then find the lowest possible.
6 - The person should be available to fight, there will be an option to press
and start the attack7 - if you don't like what you see you have a few seconds before the battle start to press and retreat without being penalized
8 - Low levels are pretty defenseless, use only a few troops to get 100%
9 - Rebuild your army, and while it rebuilds you can search for another target. You probably still have enough troops to make an easy 100% again
10 - If you keep attacking only low levels you will probably have your army rebuilt very fast.
11 - Just keep the flow.
Please comment to improve the solution as I find it'll really help getting this
(only problem is that if many people use it it will be more difficult to find targets, but I believe there are sufficient out there)