Here are two muscles that are common with headaches, the temporalis and the superior oblique. This video shows how to massage these muscles to reduce tension and headache pain.
A forward head posture is common with headache pain. A great exercise to help reduce tension and muscle guarding is nodding. This post includes a video on 'how to' treat headache pain through daily exercise.
Sometimes headaches can be relieved by neck traction. Here is a video showing how to do this on someone you care about. Remember to go slow and get feedback.