2nd: dont limit yourself by doing 3/4 reps, build up some work capacity in your tri's so you dont have them as your weak point. basically find what you arent good at and make it so you are good at it. thats why its called training. to make yourself better. cosmetic goals are great, but if you train with a purpose (strength, endurance etc) the results will come. if you know your arms are weak, then they will probably visually be so. keep that in mind with all bodyparts. if you make the bodypart you want strong, it will by default be larger.