If in doubt as to which needles to pull, don't pull.
Developing pines is a marathon, so if you have to wait while you learn (seek out sources, etc.), wait.
By the way, you never said what kind of pine you have! It matters!
Needle pulling is an advanced technique. It's kinda like... if you have to ask, you don't need to know. Yet.
All that said, a GREAT book to get is the "Pines" book published by Stone Lantern. It takes the "best of" articles from Bonsai Today magazine (which themselves are translations of Japanese bonsai magazine articles), and has it broken down by White Pines and Black Pines. It is the Bible for doing pines. You can get it for about $30 on ebay. Your local bonsai shop probably has it. If they do, buy from them They need the business.