I currently weigh 82kgs and I'm 5'11". Exactly two years ago, I weighed 108kgs; through lifestyle changes, eating healthily, doing cardio and (therefore) bumping up metabolism, I have managed to maintain this weight easily. I used to be in semi-professional swimming and taekwondo clubs, and I am very familiar with the standard workout precautions (warming up, protein intake, low GI foods etc etc.)
I have been lifting weights at home for around a year, and there has definitely been improvement. However, I'm aiming to use dumbbells to the fullest extent now, because I have finally found a gym nearby.

only exercise issue is with bicep curls. Right now, I can only curl an 11kg dumbbell about 5x before fatigue sets in. I am not entirely sure how elbow should be positioned or how far up I should lift it. Because of this, I feel there is a technique problem going on.
general fitness is decent; I can do 3 sets of proper push-ups with a 31 / 17 / 12 rep count, and can manage 5 or 6 chin-ups.
Any help would be appreciated.