The problem is that you're playing alone. GTAO is like a completely different game for me when I play alone compared to playing with a few of my friends. It's so much more fun when playing with friends.
Step 1 - Acquire friends who also own the game.
Step 2 - Either tear up free-roam with said friends, or spend a few hours rotating between missions, races, death-matches, etc etc.
Step 3 - Relax and enjoy it. Don't worry about money. Don't worry about the "point" of it. Just play it and have fun. You will have garbage missions to start of with, but they do get better as you level up. Before you know it you'll have an attack chopper of your own.