most used private ip are of the range 192.168.x.x, some other routers use 10.x.x.x, and very few uses 172.16-31.x.x (for no professional/society local networks, but for home/family local networks)
last numbers are usually attributed from lowest to highest free ones in the range allowed for dhcp on the router (fixed address must not be in same range)... once a device has been attributed an ip, the router memorize it and try to reaffect the same ip at next connection... but sometimes another device has been connected before and have received that ip, so your device may get another one instead of the previously attributed...
that's why service servers works easiest with fixed ip (from wich you are sure to always connect with same private ip, without the risk to have dhcp attributing it to another device)
hostnames are another story: each device has one wich you could decide... that hostname is used to map to ip, but there are many tools to do so... as said by Martin Taylor
you can update the /etc/hosts ^^