Weight decides the map
A trailer tows safely when the load sits in the right place, and with horses that means the greatest weight over or slightly ahead of the axles. In most trailers the front stall is also the longest, which suits the biggest horse twice over: his weight stabilises the outfit and his body gets the room it needs to balance. A small pony loaded in front with a heavy horse behind reverses both advantages — the outfit rides worse, and the pony may be standing where he can duck under a breast bar set at a bigger horse's chest height. Draw the map from weights and lengths first; temperament only decides the order you walk them up the ramp.
Ramp order: the settled horse sets the tone
Load the combination's calmest, most experienced traveller first. He walks up without drama, stands quietly, and turns loading into a non-event for everyone watching — horses take their cue from the horse already inside far more than from the people outside. After him, load in descending order of confidence, and keep the reluctant, young or restless horse until last: the final horse loaded spends the least time standing in the trailer before the journey starts, which is exactly what a fidgety traveller needs. If the nervous horse is also the heaviest, weight still wins the front stall but he loads in his turn — position and sequence are separate decisions.
Fit every stall to its horse
Partitions, breast bars and breech straps are only safety equipment when they are set for the horse between them. Shorten the stall for the small horse so he cannot turn or slip beneath the bar, widen it for the broad one so he is not wedged, and tie each horse short enough that he cannot reach his neighbour but long enough to use his neck for balance. Mixed sizes are where generic settings fail: a trailer arranged for the average of the group fits nobody in it. Walk the empty trailer before loading day and set each stall up for its named occupant.
Neighbours are part of the plan
Size order is not the only map. A horse who kicks travels best beside the most tolerant neighbour — or with an empty stall and the partition swung across if the layout allows — and mares, geldings and stallions each bring their own diplomacy. Put compatible horses adjacent, separate known enemies with the horse nobody minds standing beside, and remember the pairing that worked: the best loading plan is the one written down from the last trip that went quietly, not reinvented at the ramp with horses circling.
Unload in the order the destination needs
Decide the unloading sequence before anyone loads. The horse needed first at the destination — the one competing earliest, or the patient for the vet — should be reachable without unloading the whole trailer on a strange yard. Last-on-first-off suits rear-unload layouts; front-unload trailers reverse the logic. Either way, the plan is fixed at home, in daylight, not improvised with the ramp down.
With the order, stall settings and neighbour pairings saved in KinsLe Family Sharing, everyone helping — family, grooms, a friend with a spare pair of hands — loads to the same plan and sees the same notes about which horse fidgets and which walks straight on.