Shoulders...help

tararocks

Okay, I will be the first to admit that I am not a gym buff, until I started this journey going to a gym was at the very bottom of any to do list. I now enjoy my time at the gym, but I do not get tons of it. I focus on cardio mostly with a few of the weight machines for my arms. I do not want to meet with the personal trainer or have a complete workout set that I always do. I know this works, however, I know myself and something this stringent does not work for me and I get burned out. So to get to the point, In about 5 weeks I am going to a wedding, wearing a one sleeve dress, so my shoulders will be exposed. I am happy with my arms, they could be a little more toned, but in general they are one of my best features, however my shoulders dont reflect that. If I wanted to focus on my shoulders, upper arms over th enxt few weeks, what weight/machines should I be focusing on? Thanks for your help.