The best way to prepare for trail hills is to train on the treadmill.
When training with the bags, it’s ideal to only do as many reps you can do clean. When you feel like you’re losing control, this is when you can injury yourself. Always remember proper form over number of reps to stay safe.
Take a little time and see where you are in your New Years Resolution. Get your focus back and readjust where you see fit. Keep growing in 2019.