Base Building 101 Edit
Walls are the first part in building your base. If you surround you entire base (or at least where your colonists sleep at) with a wall and make 1 entrance then all the zombies will come to that entrance. At the entrance you can put lots of archers/guards to kill them before they can get in. If you don't make an entrance in the wall then your colony will enter "siege mode".
Towers EditTowers help give your walls shape if you make them stick out of your walls. They can also increase your archer's range (citation needed). This gives you more breathing room when dealing with hordes of zombies.
Spiral (or gauntlet) Edit
A single spiral leading to an entrance 338 blocks long will make the zombies only have one path and die before they can reach the colonists. This is based on zombies moving 1.25 blocks per second and night lasting 4 minutes 30 seconds. This strategy means you will not need colonists assigned as archer's. Note: Spiral can't be too far from banner where the zombies can spawn inside the spiral. This can also be combined with a tower strategy with archers to pick off zombies to reduce the necessary spiral size. NOTE: This does not work now that zombies do not die when the sun comes up.
One of the easiest ways to build such a spiral is to dig a 2 block deep, 1 block wide trench, forming a 67 by 67 square. At any point at the square have the entrance and exit into the trench, but separate them so Zombies will have to walk through the entire trench. Place your Banner right at the exit of the trench. Maths: 67*4+75=343>338.
Types of bases Edit
These aren't the only types of bases you can build, they're just examples.
Compound Base Edit
A compound is where everything is inside the walls. All the farms are around the walls.
A village has little to no walls and each farm plot has a house. Recommended only when the zombies are turned off for that world.
The way your beds and accommodations are laid out.
Accommodations are vertical resulting in a relatively small footprint and efficient storage
Underground living spaces are extremely efficient as no building is neccessary (only digging) and only one entrance (hole) is needed to be defended.