You can join the task force once your HQ is at level 6. Hit the task force button on the left (looks like 3 little heads in a ring), find tab, type in Arcade Otaku (we are the only task force with this name or similar). If your player name is different to your forum handle, put your forum handle in your join request or spam a lot of


Small beginnings
The in-game tutorial will teach you the basics, so watch carefully. There is no need to spend any diamonds at this early stage, but you can earn some back fairly easily if you really can't wait the small amount of time it takes the early upgrades to build.
You cannot be attacked by other players, or attack other players, until you upgrade your radar to level 2
With this in mind, it is sensible to max absolutely everything as far as you can before you upgrade your radar to level 2.
Defence
Early in the game, place your HQ tight against the docks (where your landing craft live). This ensures other players can only attack your base from one side, making it easier to defend. Trees and other obstacles do not act as barrier to attackers! Attackers can use flares to guide their troops through the forest, so your HQ must be defended from all sides.
Space your defensive towers out so that as many as possible cover the HQ whilst also covering each other. Overlapping fields of fire provide the best defence.
Avoid placing defensive towers so that they touch each other, including at the corners. A single well-placed artillery hit can otherwise damage or destroy multiple structures, giving a competent player a significant advantage against your base.
Try to place non-defensive structures near your towers, so that they don't give attackers easy pickings. All structures give the attacker extra gunboat energy when destroyed. Placing all your residences on the beach may make them look like pretty beach huts, but it'll give your attackers free gunboat energy which they can then use to destroy your base.
Here is a good example of a "docks" base;

Do not ignore your vault! The higher level your vault, the less of your resources that can be captured by attackers. This in itself will help to put attackers off and result in it being less worthwhile for players to attack.
Watch your defensive replays and analyse weaknesses in your defence. Use mines to your advantage and place them amongst your structures in the path enemy troops will likely take to get to your HQ. Always space mines at least 1 space apart to avoid them easily being picked off in groups by artillery. Large groups of mines or minefields used to create an artificial barrier are easily destroyed or simply flared around.
As you progress, be sure to consider what type of defences are effective against what type of troops. Try to ensure your base is effective against all types of attackers, rather than just concentrating on anti-troop (machineguns, rocket launchers) or anti-tank (cannons, boom cannons). Try to keep your HQ covered by at least a few anti-troop weapons to avoid being easy prey to smokey warriors.
With this said, prioritise Rocket Launcher and Boom Cannon upgrades once those weapons are unlocked. These are your most important defences and the ones attackers will target first with their gunboat.
As you progress and are able to clear away the forest and boulders, move to a corner defence (intermediate);

or beach defence (advanced);

These are sound defensive principles which force attackers to confront the majority of your defences before they reach your HQ. They allow you to better dictate the way attackers behave and protect your base accordingly.