Leaving your units unattended in your base is the quickest way to get them killed, destroyed or taken away from you! Ideally you should always be active, raiding and chasing Resources; but when you can’t, the most criminal of mistakes you can make is to leave your units open to attack!
Move your units to the protected area within the game (usually a bunker or something of that kind) when you are not using them. This is the most important step in building a huge, powerful army – and the absolute best way to surprise your enemies if they decide to bring the fight to you!
The most generally accepted practice is to leave a small number of spying or reconnaissance troops out in the “open” of your base and risk their loss in the event of an attack.
In essence, you are sacrificing the cost of those units in exchange for information on the enemy. Smaller, weaker players will generally fail in even the most basic of scouting missions, whereas the more powerful players will easily destroy your defense and plow on regardless.
The only thing is, now you know everything about their army – your battle report, or history should show you exactly how they attack and with what type of units and their numbers.
Some players spend all of their resources and energy in increasing their defense in the hope that this persuades would-be attackers into avoiding them and keeping their distance. In practice, though, this rarely works.
The vast majority of MMOs weigh their games heavily in favor of attacking and offensive actions. This is to encourage action and interactivity between players, and usually, in order for people to succeed in the game, it is a necessity to attack people.
With this in mind, the common piece of advice is to firstly concern yourself with building a capable offensive force, one which can amass resources for you and help speed up your progression in-game. Leaving too many troops out will send a message to most “hardcore” players that you are ready for – and want – a battle.
While you’re new to the game, keep your head down and try to build up while flying under the radar.