If the model is consistantly too cold or warm, adjust your numbers accordingly. Once above 7 to 10 knots the minimum temperatures are lessened due to increased mixing of the cooling air at the surface with the warmer air above the surface. Besides just preventing temps falling, the wind also advects warmer or cooler air. Moisture absorbs outgoing radiation and re-radiates it back to the surface. If the temp reaches the dewoint then latent heat is released and the low is just about halted.
Scattered clouds have a smaller effect than overcast.
The vertical distribution of temperature in the lowest few km plays a large role in determining the max temp. If the temperature increases rapidly with height, then as the warmer air is mixed downward, the temps increase accordingly. Find a sounding station nearby to get an idea of how the temp increases with height and watch how this changes and affects the high temp. To get the most out of this contest, use the model as a guide. Once comfortable with the general way the atmosphere works, try making your own forecast based on local trends and your interpretation of the model.