Three things you should not do
1. Do not open every resource in your bag.
There is a tendency for people to want to open packages, its an opportunity to gain shiny new things. But do not do this. While resources are packed away in your bag of holding they are protected against someone attacking your sanctuary and taking them.
When you look in the resource shop you can see which resources are protected and which are not.
Your warehouse will protect a specify amount of resources based on your level. This however, is ultimately capped by your level. This means anything over that amount is unprotected.
When you are over your resource cap, and you open those shiny resource packages you are making yourself a ripe target for someone to hit you.
If they scout you and see that you have a lot of resources unprotected it you could gain the attention of a resource hungry player.
So although you may be tempted to open all those pretty packages of food, wood, steel, and gas, its best to leave them where they are until you actually need them. The game will prompt you to auto use the resource when you need it.
2. Do not resource grab a tile that is occupied
The world is full of these resource tiles: food, wood, steel, and gas. Most people observe the right of first in. If you have secured the tile and your troop line is connected to it, then its your tile. Obviously the same is true of other players.
There are plenty of tiles on the map at all different levels, however normally people will grab the higher level tiles immediately preventing others from grabbing them. In some states I’m sure people fight over them, but I expect most people play by the first in rule. So if you do not want someone else kicking you off a tile you have occupied, you probably shouldn’t go about taking others occupied tiles.
3. Do not leave a tile with resources remaining on it.
You see here someone has left a tile on the map with resources left on it. Each hour tiles regenerate on the map, but only if they have first been cleared off. When you take resources from a tile but leave some left over you are basically making it so that the tile will stay there until someone else takes the scraps you left.
This is a big faux pas, do not do this. Take all the resources or if you lack the troops, try a lower level tile to gather from instead. Anyone who is searching for a level 6 or 7 tile is going to be angry if they find an unoccupied one that only has a few thousand resources on it. And either they will have to clear that taking time and effort to do it, or they will leave it for some other person to do it in which case it may not clear for a long time.