Buy a digital thermometer. I bought a weber one for about $20. You set what type of meat you are cooking and it sets the temp alarm automatically. Even to what how you like your steak cooked, rare med etc.
I use a gas cooker as it's easier to regulate. I would say get to know your BBQ. like an oven they can have hot spots. If you're cooking chicken put it in a bowl and cover it with Butttermilk and leave overnight if possible or at least 3 to 4 hours. Dredge the chicken in seasoned flour. Turn off one side of BBq or move coals to one side and cook chicken away from direct heat. Insert thermometer in biggest piece and close lid check half way through and turn. Thermometer will ring when temp gets to 165F open lid take out chicken and let rest then serve.
If doing a steak. Sear it, move it off direct heat close lid and let cook. Burgers cook on one side for about 4 mins then turn once and cook other side for 5 to 6 mins for med to well done. Top tip for burgers is to buy steak and get your butcher to mince it in front of you. I make the best chilli burgers from scratch, people always come over to my BBQ and never any food wasted
..... fascinating I know.... but true! 
.... it went down a treat with lashings of cream poured over it! 
