Before discovering any free-mount techniques (without any support), focus on learning the basics, just riding along.
Find a fence or a hand rail that is easy to grab and that you'll be able to hold onto during your first desperate attempts at riding a unicycle.
Choose your front foot
Identify the foot that will be your driving foot (on the forward pedal when idling). This is usually the foot that you would naturally keep forward when cruising on a bike, or the foot that you would stomp forward when you trip over a step.
Always keep some pressure on both pedals
Holding firmly onto a hand-rail or fence, mount on the unicycle and put as much weight on the saddle, while applying equal pressure on both pedals. Once you have reached a stable position, seating upright and aligned over the cranks, try to rock forwards and backwards by alternatively applying more pressure on the front and back foot. Don't look at your wheel as it will kill your sense of balance. Instead, look at the horizon, that's your reference. Practice this idling and progressively release your grip off the fence. After some hours, you should be able to let your support go, and idle on site. The next step is to complete pedal turns and ride along the fence. Keep in mind that regardless of what foot you have in front, you must always counter-balance the pressure on the front pedal with back-pressure with your foot on the back pedal. When you ride, this front/back pressure on the pedals swaps from one foot to the other every time the crank arms pass the vertical position. This constant pressure on both sides of the crank will keep the unicycle stable and prevent it from shooting off underneath you. As you gain confidence riding along, holding the fence, progressively let it go until you can ride along the fence without touching it. Then try out different terrains, but preferably in areas where there is nothing to break or crash into, because the first attempts will be quite more difficult than learning to ride a bike.
Riding Seat-in-Front (SIF)
Most of the techniques in unitrials can be done with either with the seat under you (Seat-In) or riding with the seat in front of you, whereby you hold/push the seat in front of you. It takes more balance and effort to ride SIF, but it is a very useful skill. With the seat in front, you gain more flexibility for crouching and jumping up sideways, without upsetting your precious flesh.
A regular free-mount, front foot first
1° Put your front foot low on the pedal, while grabbing the uni by the front of the seat. Pull the seat under your groin.
2° With a push of your back foot, thrust yourself over your front foot, standing on the bottom pedal.
3° Aim your back foot over the other pedal. The quicker you'll get there the better as you are only balancing on one foot.
4° Firmly push the top pedal backwards, but don't kick it.
5° This gets you rolling back and readjust the uni under you.
6° You end up with both pedals level, your good foot in front.
Ride off immediately or start idling or hopping. Keep most of your weight on the seat, not on the pedals. See the move in a video
Once you are off riding along, don't hold the seat as this will put you off balance. Instead, spread your arms to use them as balancing poles or counter-weights. If you keep your weight mainly on the seat, it won't slip off. If you fall sideways, turn into the direction of the fall and re-adjust your balance immediately with a back and forth swing. Try different surfaces to ride on. Very smooth surfaces are less forgiving as the uni will tend to roll off under you very quickly. Well seated on the uni, rely on your hips to control the turns but use your arms to balance sideways.
You can initiate your turns with your arms (to build momentum) and follow up with a twist of the hips. To hop on site, stomp on the unicycle and firm up the ankles and legs in a quick extension. For balance correction or changes of direction, try to limit the height of your hops to a minimum (ideally, you just need to relieve the tire from the ground). No need to grab the seat, unless you want to hop high or drop off or play specific tricks. Also practise your pedalling and experiment with front/back pedal pressure at different angles on a slope. Facing a slope up will require more pressure on your front pedal, whereas facing a slope down will require more pressure on your back pedal (as your feet alternate, you'll have to constantly change the pressure).