1. Never leave your bike's fuel tap on when you are not riding.  This is especially important for the journey to a trial - the vibrations cause fuel to leak into the cylinder and wet the plug, and it becomes difficult or even impossible to start the bike.
2. Use a new spark plug at the trial.  Nothing beats the ease of starting, the reluctance to stall, and the pure performance of a new spark plug.  Since plugs are about R35 each, it is worth it to have a new one every monthly trial.  One strategy is to fit a new plug for the trial, then swap it out
   

In a two-stroke trials bike, we generally use 15ml of two-stroke oil to 1l of petrol (i.e. in a 5 liter fuel can, add 75ml of oil, and in a 10l can add 150ml.

Follow the instructions in the bike's User Manual.

Also, be aware that not all two-stroke oils can operate at such low concentrations.  For example, Castrol Power1 Racing synthetic oil is not rated at such low concentrations.  I use Ravenol synthetic.  Be especially wary of cheap oils, but check whether an expensive oil is rated at 1:66 mix ratios.

Front: 0.5bar (50kPa)

Rear: 0.3bar (33kPa)

Naturally, this is average.  If you are riding on sand, mud or low traction surfaces, you can go lower than that.  If you are quite heavy, riding rocks and hard edges, or generally hard (aka a bit clumsy) on a trials bike, increase the pressure slightly to protect the rims.

The idea is that the person who puts his foot down (a dab) the least often is the winner.

Dabs (1 point)