Pre-juice is what we call "priming" a coil. To prime, all you have to do is to put some e-liquid onto the wick of your coil before putting it into your tank. Then, once you have it in your tank full of juice, let it sit for a few minutes (I prefer to let it sit for at least 5 minutes or more). This will let the wick get thoroughly soaked in the liquid so you don't get a dry hit and burn up your coil.
As for how much power to use, start low -- I would go with 10W and vape. If it's not doing it for you, bump it up a little, vape. Repeat in small increments until you get the vape that works for you. There is also a breaking in period on some coils so once you get the vape you want, vape on it a little until it gets broken in properly.
One more thing -- on your tank -- if you're using a high VG liquid, make sure to open up the airflow. If it's not betting enough air, you run the risk of getting dry hits.
Good luck and welcome to Vapor Talk.
