Not much I can add except experience. Like others have said, soft straps with ratchet straps around crash bars at front, panniers at back, forks half compressed. Be sure not to let the straps touch on anything that can abrade them.
My ratchet straps and soft straps came from Amazon. They're 1-1/2" wide and rated for 1000 lb working load.....are way overkill I'm sure. I had no trouble at all hauling my bike 1200 mile round trip.
If there's a wheel chock, running the straps from the back (top of pannier racks forward to the front of the trailer deck works surprisingly well (backup set from crash bars also forward). I never wouldathunkit, but TenereGuy showed me...and we went another 1200 mile round trip doing that.