I suggest you sit down and envision in your minds eye your enemy and then create a sigil based off of the way you see them. What I mean by see is try focusing on your hated for them and develop a sigil based off the way they treated you. It can be as simply or as complex as you feel comfortable...

Hail King Satan, Hail King Lucifer. Hope your meditation goes well, stay strong and good luck!

I suggest a basic casting of the circle ritual. Basically you just open up a circle, light four candles, and meditate while envisioning King Satan. After some time of meditation speak out to them and they will respond. The first time I did what I just described the Demonic Gods I was talking to...