By using the subnet mask you can work out how many address are in a given range. For instance in a /24 (mask 255.255.255.0) you have the whole of the last octet to play with, well, apart from the first and last addresses which will always be your network address and broadcast respectively.
So for your example:
192.168.1.0 – Network Address
255.255.255.0 – Subnet Mask
192.168.1.255 – Broadcast Address
192.168.1.1 to 192.168.1.254 – Useable Addresses
Your default gateway is already .1 so really <b>you have .2 to .254 for use</b>.
I would suggest until you have learned sub-netting have a quick search on google and either use an online subnet calculator or download one of the many free ones. There is a great online one at: IP subnet calculator
are you using DHCP? If you are then you can see what are the IP’s that are not used yet
if not just ping the IP that you feel like using..