As I've been doing a bunch around cameras, streams, security, I wanted to make sure I can move my Raspberry Pi around with out worrying about the IP address changing. That's really because my house has a pretty decent router that protects from incoming traffic.
But I've added some redirects and port forward, to allow certain things through, but securely :). Well, setting the IP address on the Pi wasn't obvious, at least not to me. So here's a few steps:
sudo nano /etc/dhcpcd.conf
Then to change the wifi connection to a static IP, add this (or modify that file)
interface wlan0
static ip_address=192.168.0.200/24
static routers=192.168.0.1
static domain_name_servers=192.168.0.1