Tips for building upper body strength?

Im trying to be more regular about working out but in the past its been really hard for me to build upper body strength. When I was weightlifting regularly (5 days/week) I saw definite results in my legs and a little bit in my stomach, but Id really like to build some strength in my arms and for some reason I just cant. I do 3-4 lifts per muscle and 8-12 reps depending on the lift. Right now for example my arm day is 4 bicep lifts and 3 triceps. And I have good quality protein powder for post-workout shakes. Idk why my lower body seems to get strongee while my upper body stays the same but I really want my arms to catch up to my legs lol!