Everyone here has offered very good advice, but I will go through my process which has only failed me once (in the freezing cold rain).
1. Take your coal basket and fill it to the top with coals evenly spread out.
2. FROM THE BASKET take exactly 40 pieces of charcoal and put them in your chimney starter.
3. Light the chimney starter as you normally would.
4. When the coals are a little more than half gray pour them evenly over the coals in your basket inside the cooker.
5. This is the only step I OCCASIONALLY deviate from, but depending on how hot I want the initial temp in the barrel, I wait anywhere
between 7-13 minutes before I put the lid on and start cooking.
6. If I'm cooking a butt, chicken, tenderloin, leg of lamb etc. I will run my probe wire through one of the re-bar holes and into the
meat.
If I'm doing ribs, I don't really pay attention to temps. Instead I follow a variation on the 3-2-1 method. I hang them for 2.5 hours. Then I wrap in foil with apple juice for 1.5 hours. Then I unwrap and sauce for 30-45 minutes.
I hope this helps someone, I don't remember where I got the 40 coal in the chimney idea, but it has worked very well for me. I have yet to try it, but i eventually want to try putting the lid on right after I pour the hot coals on. Maybe that will give a lower barrel temp for beef ribs and what not.