I'm new to Fallout Shelter, and I'm not doing well. If I start over, I may make the same mistakes, so I'd rather learn how to pull myself out of my hole (no pun intended.)

I've got 19 Dwellers, 3 rooms worth of power generators, 3 of diners, and 2 of water treatment rooms, plus 8 others.  However, I'm very low on food and water and I can't seem to make any progress. I'm building stimpacks and those rad cures as fast as I can, but everyone is sad-looking and overall happiness is 10%. 

Somehow I've managed to accumulate 2000 caps, and I know I should increase my production of food, water, stimpacks, rad cures, and babies. 

Where should I focus my efforts first?