The default DHCP setup is dependant on the "Use DHCP Allocator" option. We will assume you are using the default 192.168.3.x IP block. If you are using another IP block, you should adjust all IP's noted below accordingly.

When the "Use DHCP Allocator" option is turned on

Device running WMWifiRouter: 192.168.3.1
Statically configured clients: 92.168.3.2 - 192.168.3.31
DHCP configured clients: 192.168.3.32 - 192.168.3.254

For static clients, use the following settings:
IP address: 192.168.3.2 - 192.168.3.31
Default gateway: 192.168.3.1
DNS (Name) server: 192.168.3.1

When the "Use DHCP Allocator" option is not turned on

Device running WMWifiRouter: 192.168.3.1
Statically configured clients: no reserved addresses
DHCP configured clients: 192.168.3.1 - 192.168.3.254

If you still want to use both statically configured clients and clients configured by DHCP, we'd advise starting the static clients at 192.168.3.200 or something similar. This will minimize chances of IP collision with a client configured by DHCP.

For static clients, use the following settings:
IP address: see comment above
Default gateway: 192.168.3.1
DNS (Name) server: 192.168.3.1