What is your object of meditation?
B. Alan Wallace suggests resting the attention on the breath at the abdomen to help with tension in the head and body. On the in breath, place the attention at the abdomen, make sure you aren't "visualizing" this. For me, I notice my eyes have a tendency to "look" down toward my abdomen, so I try to relax them and keep them straight ahead. On the out breath, relax anything in the body that you notice as being tense. Keep letting go of the out breath and relaxing until the in breath comes on its own without being forced. Continue this cycle of focus and relaxation, bringing your attention back to the abdomen when the mind has wandered; Release, relax, return.
B. Alan Wallace has some extensive guided meditations on media.sbinstitute.com. I highly reccomend them.
Cheers