Finding ESP8266 in a network
Some solutions that have worked for me:


Reserved IP - use the router's DHCP reservation to give the same ESP the same IP each time.
Static IP - Set the ESP to use the same IP each time, bypassing the DHCP feature altogether. This also boots the ESP slightly faster. WiFi.config(ip, gateway, subnet);
Dump the IP address to Serial on boot, so that you can at least see what's assigned: Serial.println(WiFi.localIP());
Give the STA a unique name that you can find in the router's DCHP clients page: WiFi.hostname("look_here");
use mDNS to assign a domain-like local URL to the device: MDNS.begin("esp8266");// default to "http://esp8266.local/"