Replying to DSLR Help/Edit Critique

So me and a friend just made our first edit with a dslr (Cannon T2i) and I was looking for advice on how to make it better. My first issue is that the majority of the shots came out super unstable and shaky. Does anyone have any ideas on fixing that? Should I invest in a handle to hold it? I also noticed the lighting was bad in a lot of shots, I'm guessing I need to play with the ISO settings to fix that? Any other advice would be great to help me get through the learning process of filming. We realized theres a lot more to it then just pointing and shooting with a gopro haha. Thanks!