It's definitely worth doing some practise loads, so the pig(s) know the trailer's okay - and probably expect to find treats or their evening meal in there

They won't like any lack of stability in the ramp or trailer, so make sure it's very firmly positioned and can't tip, and the ramp is fully supported so won't bounce or wobble. (First time I loaded a full-grown pig, I hadn't accounted for the weight of the pig in the back of the trailer, and as she climbed in, the nose wheel left the ground and pointed at the sky! So support it front
and back if it's not connected to the car when you load.)
I put a heavy mat on the ramp to load my pigs - they didn't like the supposedly 'non-slip' metal surface, and strawing it didn't help much, but they are happy with a nice grippy carpet or mat. Of course make sure it won't slide about.
I always load the pig(s) the night before, give them a light last feed as they load, and a drink which I take away at bedtime. Lots of straw to snuffle about in and make a comfy bed in. Then just drive away in the morning - they usually don't even notice and sleep all the way to the abattoir. In fact I've had several so relaxed I struggled to get them to come out of the trailer! (Not through being stressed or scared, just through being comfortable and happy.)
At our abattoir they generally do go straight through, but they are unloaded into large strawed pens at first, so of course they get busy snuffling and rootling, far too busy and inquisitive to worry about where they are, why and what's going to happen next.

If I have to take one pig somewhere, which sometimes happens, I still load it the night before but I have the trailer where it can hear and talk to other pigs. (Which may mean other pigs spending a night in the byre, but they don't seem to mind.) Pigs are always reassured if they can hear another pig

If you load earlyish in the evening the night before, you've got all the time in the world and you don't get stressed and anxious if the pig doesn't load straight away. If you leave it till morning, you have time pressure on you, so, livestock being livestock, that's precisely when they will decide not to load.

And you can't bodily lift a pig, or 'shoo' it, the way you can sheep or cattle.