Always keep the exhaust stack wide open. Control heat with inlet dampers and amount of fuel.
I have a 36" offset with 1/4" steel. It's hard to heat that much mass up with just charcoal. In my first run with my smoker I used charcoal and chunks and couldn't keep temps past 210. I also had a few design flaws that needed tweaking. Now I burn just wood and can easily get 325+
I would suggest starting with a little charcoal or lump that is pre-lit in a chimney. Then you add wood splits on top from there to get a real fire going. The more wood you add, the hotter the fire gets. I usually have splits about 6"-8" in length and 2-3" in diameter. I will stack them on top of my charcoal to get my fire going. And through the entire course of the smoke I just burn wood. Eventually the charcoal burns out but you will have created a bed of embers from the wood. The trick is keeping the ember bed going by keeping your fire continuously burning. I stack the wood criss crossed - 2 logs parallel to each other about 3"-4" apart on top of the embers, and then lay 1-2 splits across the 2 bottom logs perpendicularly. That type of stacking seems to really generate a lot of heat for me. The more wood I stack on, the hotter the fire gets. And of course you also adjust dampers for further temp control.
Also, did I mention keeping the ember bed going? This will ensure you constantly have burning logs, not smoldering logs. Smoldering fires will put off creosote. You want to have a hot burning fire.