Put your seat as high as comfortably possible. You know the rule for setting the seat height on bicycles: sitting naturally with a comfortably straight leg and your heel on the pedal gives you the right height. I find a tad lower works better for the unicycle - maybe only 5 - 10 mm lower, but it makes a difference.
Sitting tall in the saddle will make the uni more stable - think of it as a Sitting tall (bum in, head up) gives it a longer period of oscillation.
Keep your weight on the saddle, not on your legs. Even a “huge” 36 is only equivalent to below bottom gear on most road bicycles, so your legs shouldn’t need to be working hard until you get to a hill or rough ground.
Think about keeping the unicycle under you rather than keeping yourself on top of the unicycle. My older son says this is the piece of advice that helped him most.
Think about that thing where you balance a broom on your finger. Small gentle movements of your hand will keep the broom balanced with very little effort. If you make big movements, you will need to correct them, then you will overcorrect and you will start to waste energy.
Look at the ground 20 or more metres ahead, or even at a fixed point in the middle distance. Looking down at the ground immediately ahead will make your balance worse, translating into harder work for your legs.
When I was learning, I looked for places like parks or nature reserves where I could ride on smooth paths until I was bored, then on rough ground or rough paths until I was tired. I could then alternate between the two, getting the useful practice on the rougher parts and getting my breath back on the smoother parts. The more you ride, the more things will come within your personal definition of “smooth ground”!
I also found that brief bursts of “top speed” between longer sections of “just cruising helped”.
The last two techniques (smooth/rough or fast/slower) work on what I’ve heard rock climbers refer to as “the dance floor effect.” They climb to a precarious ledge. They then climb up to an even more precarious one, and retreat to the original one to think about their options. Each time they return to the original precarious ledge, the easier it feels, until eventually it is “like a dance floor”.
Also, find an area like an empty car park, tennis court etc. and set out some markers (cones, bags, your jacket?) and ride figure 8s so that your brain starts to work on the steering and forgets that the fore/aft balance is difficult.
As with all balance and fine motor activities, the end goal is to take your mind out of the equation and leave your brain to get on with it. By the time you’ve consciously thought of something and put it into action, the moment has gone.
Good luck, and have fun with it. If you are confidently riding a couple of miles at a time, you have already achieved more on a unicycle than most people in the world. You’ve done the difficult bit, now it’s just refining and developing it.
