What is the best way to load freight on a tractor trailer?

It depends on what the freight is and what the trailer is. If it's vehicles, you typically drive them on and off. If you have a van trailer with sliding tandems, you would ideally want the weight distributed fairly evenly between your drive and trailer axles. If you had a trailer with spread axles, you would want more weight towards the trailer axles, since you're allowed 40,000 lbs. on a set of 10 ft. spread axles, as opposed to 34,000 lbs. on your drive axles.