You set them to forward fire. However, the only reason you would purchase turret mining laser, other than for multi-crew, is if the regular mining lasers are not available. Unless you plan to perform mining in multi-crew, go with the fixed mining lasers.
Don't forget your Collection Limpet Controller (two if you have a large enough ship), and about 50% of your total cargo in limpets. If you have the Prospector Limpet Controller, then you may want to push the limpet cargo to 60-75% of your total cargo capacity.
Personally, I like the Python for mining. If you have the money to fit one out, it is definitely a great ship for mining. Enough modules to hold 2x 3 size Limpet Collection Controllers, a Prospector Limpet Controller, a Size 4 module Refinery, 220 cargo, and enough fire power to effectively defend yourself against NPC Wanted targets. You can fit everything you need with a 6A power plant do you don't have to splurge for the 7A power plant, and that saves you a great deal of money. It cost me 115 million to load out mine. Let me know if you need specs. Have fun!