Before attacking another player, always do the recon option first to see what they have. Level up your recon in the research lab to get more information. You want to find out what they have on their walls, as well as what troops they have, in order to make sure your team is stronger than their team. Plus, you want to see what resources you can get, because if someone doesn’t have all that many resources, it’s not going to be worth it.
It’s never going to be worth it, though, if the other player has a storage bunker that has been upgraded to a high level, because this will protect literally everything except for their coins. The only way to know if an opposing player’s resources are unprotected is to attack them and then see what you get. If you somehow come across a player with a lousy storage bunker, then keep raiding them and stealing as many resources as you can.
An infected city, though, is impossible to perform recon against. You have to guess to see if you can raid them successfully, because you never know how many troops they have, so to take an infected city, send in whatever number of troops that you would normally send in against a player of the equivalent level, except send far more troops just to be sure.
Once you clear out an infected city altogether, it will turn into a deserted city. A deserted city will have no defenses whatsoever, but will have all five of the resource types. Once you have a deserted city at your disposal, farm it as much as possible.
Find a place that you love to farm? Write down the coordinates so that you can always go back to it later. The coordinates will be on the right hand side of the screen whenever you tap on the city or location – for example, there will be an X coordinate, a Y coordinate, and an R coordinate. The R will always be the same because it represents what server you are in, so write down the X and the Y.
Want to get the most troops that you can? Then always have both your recruiting station and your wall going at the same time to train troops at double the speed, thus allowing you to constantly roll out large numbers especially on defense. As we all know, fighting other players is a numbers game, so this will help you to defend against other players easily.