OK, you're a warlock, which is a striker role. Your function in a fight is to identify the worst threat and take it down, but you can be kind of squishy so you need to do it without getting pinned down and squashed. That said, you can and should take a hit or two every now and then to take some of the presssure off the front line.
You'll want to move around the battlefield for three reasons. First, every round you can curse the nearest enemy, and you want them all cursed so when they die you get something cool. Second, you get a +1 to attack if no ally is closer to the target than you are, and once or twice in every fight that +1 will mean you hit instead of miss. Third, you see that daily power, Armor of Agathys? Well, here's what it's for...