your brand new NEXTAR should be run rich the engine is set rich so it doesn't burn up on you and you don't need to go through the "break in procedure",if the engine is bogging then don't let it idle for long,if you keep the revolutions up it shouldn't load up on you.
you should run at least 5 tanks through it either on the ground or preferably in the air.
if you don't know what your doing then STOP! and get some help from someone who does.
bruce88123 gave you some good advice the engine is rich for a reason the low end is set rich and after a few tanks it should be leaned out just a touch ,read the NEXTAR instructions page 21,and familarize yourself with the OS hand book that came with your plane.
there is 2 main adjustments the high and low speed needles.
the high is the main adjustment and has the limiter on it,the low speed is the small screw in the barrel in the carb and is sensitive to adjustments,when you adjust the low speed needle you need to retune the high there co dependent to run well.