hey bro,how are you? i'm going to give you a tip that i wish was given to me when i first started. 20 is kind of light, really it is too light. do this, first find out what you can press for 1 time, then get the weight that is right below that. start heaviest on your first set, then work untill th lightest. YOU HAVE TO STRAIN HARD IN ORDER TO GAIN STRENGTH AND SIZE! do every set( 4 sets) 6-8 reps. GO HEAVY, DONT BACK DOWN FROM HARD TO LIFT WEIGHT, TRUST ME, YOU WILL UNDERSTAND THIS IN THE FUTURE!
good luck and welcome to the bodybuilding world!