Originally from https://gist.github.com/mattiaslundberg/8620837. Copied here for my own archive.

Configure the wifi:
<code>
wifi-menu
</code>

Create partitions with fdisk

Setup the encryption of the system
<code>
cryptsetup luksFormat --type luks2 /dev/sdaX
</code>

Open the partition and make an ext4 file system
<code>
cryptsetup open /dev/sdaX cryptroot

mkfs.ext4 /dev/mapper/cryptroot
</code>

Mount the new system 
<code>
mount /dev/mapper/cryptroot /mnt # /mnt is the installed system
mkdir /mnt/boot
mount /dev/sda2 /mnt/boot
mkdir /mnt/boot/efi
mount /dev/sda1 /mnt/boot/efi
</code>

Install the system also includes stuff needed for starting wifi when first booting into the newly installed system
Unless vim and zsh are desired these can be removed from the command
<code>
pacstrap /mnt base base-devel grub-efi-x86_64 zsh vim git efibootmgr dialog wpa_supplicant
</code>

Setup fstab
<code>
genfstab -pU /mnt >> /mnt/etc/fstab
</code>

Make /tmp a ramdisk (add the following line to /mnt/etc/fstab)
<file>
tmpfs	/tmp	tmpfs	defaults,noatime,mode=1777	0	0
</file>

Enter the new system
<code>
arch-chroot /mnt /bin/bash
</code>

Setup system clock to local timezone
<code>
ln -s /usr/share/zoneinfo/America/New_York /etc/localtime
hwclock --systohc --utc
</code>

Set the hostname
<code>
echo MYHOSTNAME > /etc/hostname
</code>

Update locale
<code>
echo LANG=en_US.UTF-8 >> /etc/locale.conf
echo LANGUAGE=en_US >> /etc/locale.conf
echo LC_ALL=C >> /etc/locale.conf
</code>

Set password for root
<code>
passwd
</code>


Configure mkinitcpio with modules needed for the initrd image
  * Add 'ext4' to MODULES
  * Add 'keyboard', 'keymap' and 'encrypt' to HOOKS before filesystems
<code>
vim /etc/mkinitcpio.conf
</code>

Regenerate initrd image
<code>
mkinitcpio -p linux
</code>

Setup grub
<code>
grub-install
</code>

In /etc/default/grub edit the line GRUB_CMDLINE_LINUX to GRUB_CMDLINE_LINUX="cryptdevice=/dev/sdaX:luks:allow-discards" then run:
<code>
grub-mkconfig -o /boot/grub/grub.cfg
</code>

Reboot