I start with the pin tombstoned, the edge of the truck about a foot away, then gently lower the pin onto the trolley. When the pin touches the trolley, it does tend to push the trolley back a bit, but at this point I lower the front quite quickly, so that most of the force is acting down rather than horizontally & it kind of automatically sits on the trolley with the front of the machine neatly at the end of the trolley (It occasionally pushes against the handle, but that extra push is very gentle, and I realise that the quicker bit was too quick).
Also, if you haven't got the trolley under the balance point, it won't fall off, as it will stay with the back edge still on the floor - at that point decide whether adding extra weight at the front is reliable enough to get the legs on.