Hi John and Gang,
I have been away from this board for but may have time to start posting again more regularly. Our tai chi school has a heavy bag in the front room. It always worked for me and I now help newer students become acquainted with it. After a student learns form the heavy bag is one of the next logical steps in progression. You can begin by simply pushing and rolling it around, but pretty some you can start hitting it. the bag won't lie to you. If your alignment is off it will tell you. If your shoulder is up it will tell you. When you gain more power you will know.
My favorite is brush knee as the palm lines up best with the bag. My brush knee power maximized pretty quickly. Press and push are good too. Fan through back is ok, but you'll get even more power on your partner once you can stick and pull a bit with your other arm. Same for fair lady, but that produces more pop on bag than fan does. Same maybe with high pat on horse. Part of my point is that much of what you can accomplish with the bag is dependent on the shape of the bag. That said, if you gain power in one move using the bag that might transfer to something you didn't/couldn't train on the bag. for example I twist the back foot at the moment of impact in the brush knee. The bag can tell me when that's working.
Punches are good, but wear at least gardening gloves at first. Straight punch is best on bags, hooks and back-fist less so. Uppercuts are good but you may scrape skin if inexperienced. Maybe use some Dit. Heel kick is good. Separate feet kick and other toe/front kicks are ok to bottom of bag if bag hangs high enough. Our current bag hangs very low and is very heavy. Sweep lotus is so so.
Also, when I peek in the windows of kickboxing gyms I often see people hit the bag and they move while the bag stays put. I want to tell them it should be opposite. Make that bag swing - that's why I don't like floor mounted bags. We have always had have these old Fist brand chest protectors advertised to make your body into a human heavy bag. Sifu just had to repair them all. I think they stopped production of those. So the next logical step is for you and your partner to work with those on.