You can include the IP of your server with the following format:
Code:
v=spf1 a mx ptr ip4:190.190.190.190 include:domain.com ~all
Notice the 'include' is for the domain not the FQDN of your server.
You can use the setup wizard on this page:
SPF: Tools and there are plenty of tools on the internet for testing the records syntax such as these:
SPF Query Tool MXToolBox - Sender Policy Framework (SPF) record lookup