Our kitchen cabinets are dark brown and I believe are made of formica. What is the best way to paint them? Do we need to use a deglosser on them? What is the best primer and paint to use? Any advice would be appreciated. Thanks!

You need to scuff the laminate with sand paper (60-100 grit) A oil base primer would work the best. After its fully dry then you can paint.
Check your local paint store. I do believe there are paints for kitchen cabinets that are more durable than trim paints.