Some fluctuation is to be expected. The key is not to over react to the fluctuations. An adjustment to the intake on your firebox will have a bigger affect than you expect, so keep things small to start out. I would suggest never closing more than a quarter of the way at a time. Give the temps 30 minutes or so to level out after an intake adjustment.
It is better to adjust your heat using your intakes instead of your exhaust. Closing off the exhaust to much will result in stale smoke being trapped inside, so make sure that your exhaust is always opened more than your intake.
As long as you can keep your temps between 200 and 250, you should be fine. As you use your new smoker, this range will shrink down and you learn the proper amounts of fuel to use and how the temp fluctuates as it burns down. Part of the fun of this is standing around outside, drinking your beverage of choice, and watching the temperature guages. Enjoy the outdoors and the heat radiating from your new friend!!