you've been training for four months. If you are just starting out, your body is starting to get toned up to "weightlifting". You have three days to work out so, break up your routine with two bodyparts a day: Chest and shoulders one day, arms and forearms day two; back legs day three. Warm up with stretching exercises. Begin each body-part with light weights to warm the area up. For chest-bench press, 3 sets for reps of 8-10; dumbell flys 3 sets for 8-10 reps; incline bench presses, 3 sets, 9-10 reps. Shoulders- behind the nick presses, warm up with light weight; 3 sets with 8-10 reps; front presses 3 sets with 8-10 reps; lateral raises with dumbells, 3 sets 8-10 reps.
Day 2 -- barbell curls with light weight to warm up then 3 sets, 8-10 reps ; alternate with tricep behind the neck extensions, 3 sets 8-10 reps; seated dumbvell curls 3 sets, 8-10 reps; alternate with tricep dips on bench or parellel bars, 3 sets, 8-10 reps; concentration dumbell curls, 3 sets 8-10 reps, alternate with close grip barbell presses lying down on bench, 3 sets 8-10 reps . Finally forearms, seated forarm curls with barbell, 3 sets 8-10reps; reverse curls standing with barbell, 3 sets 8-10 reps; dumbell forearm curls seated, 3 sets 8-10 reps; and reverse dumbell curls standing, 3 sets, 8-10 reps.
On the last 2-3 reps do a weight you can feel the "burn" in the muscle worked. Hope this helps gets you moving towards gains.