A new player will enjoy a 24-hour shield. Use that time to start tending to defensive concerns, because you're likely to come under attack once that period of protection passes. Make sure that you strengthen your outer wall and train troops in particular, though you might also want to set a few traps. If you don't plan for enemy players to attack you, it'll hurt worse than normal once they inevitably do.
Allies Matter
Make sure that you're working on an alliance mission at all times, which of course requires that you also be a member of an alliance. You don't even have to do anything active to complete the missions; just accept the mission and let the game take care of the rest, until it's time to collect a reward.
Base layout
Strengthen your base with as many defenses are possible. When first starting, you will be under a twenty four hour protection period that keeps you safe from attacks from other players. Use this time to build defenses. Upgrade your wall, place traps inside, and enough troops to defend your base.
Commander
Your commander's skills allows him to directly influence your base's management and troops. Each time the commander earns enough experience, he will level up and earn some points. Spend those points in skills that are both base and combat types.
Commander Leveling
You should make sure not to neglect your commander. Level him up whenever possible to acquire points that you can assign to improve your base and tactics. You won't get far with a weak commander!
Grab the Supply Crates
Near the bottom of your screen, you should see a bouncing box. Open it to collect random goodies. You can open it frequently, though each time you do, you'll have to wait a little bit longer before you can do so again. There's no telling what the crate will contain, so definitely open one whenever you have the opportunity.
Tend To Main Missions
It's easy to get distracted and start ignoring missions that are recommended at the bottom of the screen, but that's not a good idea. When you complete them, you'll be able to upgrade your base with additional buildings and defenses, or you will receive exciting rewards, so you shouldn't let mission completion fall by the wayside.
Upgrade Facilities
When you can upgrade a facility, take that as a sign that you should do so immediately. Farms, mines, oil wells, and similar facilities are critical to your war effort, since they'll allow you to keep your other efforts moving forward, so make tending to them a priority.
A Strong Defense...