Use a good primer that is recommended for paneling. Check at Sherwin-Williams, Kilz and/or Zinsser - they all have high quality primers for paneling. I have used all 3 brands succesfully. You also want to get a good quality paint for the topcoat. On very dark paneling I have used 2 coats of primer then 1 coat of topcoat for excellent results.
Painted paneling will look nicer than you might think. If you take your time to do the job right and use quality materials.