Document IP addresses or us an IPAM
Document your IP scheme, VLANs, and static IP assignments.
For small networks, an excel spreadsheet may be sufficient.
For larger networks, I recommend an IP address management tool. For years I used an excel spreadsheet and as the network grew the spreadsheet became a nightmare. I eventually moved all the spreadsheets to SolarWinds IP Address Tracker and no longer worry about IP management. SolarWinds IPAM takes care of everything for me and best of all I can quickly search the entire database.

IPAM Benefits
- Automatic IP address tracking
- Can integrate with DHCP/DNS to track dhcp scope usage
- Alerting and reporting of scope usage
- Search IP addresses, comments, hostnames, etc. It is so nice being able to quickly search by a keyword to see what a device’s IP address it.